Aristotle's On the Soul: Entire

ON THE SOUL by Aristotle
Public Domain English Translation by J. A. Smith

Book I

1

HOLDING as we do that, while knowledge of any kind is a
thing to be honoured and prized, one kind of it may, either by reason of its
greater exactness or of a higher dignity and greater wonderfulness in its
objects, be more honourable and precious than another, on both accounts we
should naturally be led to place in the front rank the study of the soul. The
knowledge of the soul admittedly contributes greatly to the advance of truth in
general, and, above all, to our understanding of Nature, for the soul is in some
sense the principle of animal life. Our aim is to grasp and understand, first
its essential nature, and secondly its properties; of these some are taught to
be affections proper to the soul itself, while others are considered to attach
to the animal owing to the presence within it of soul.

To attain any assured knowledge about the soul is one of
the most difficult things in the world. As the form of question which here
presents itself, viz. the question 'What is it?', recurs in other fields, it
might be supposed that there was some single method of inquiry applicable to all
objects whose essential nature (as we are endeavouring to ascertain there is for
derived properties the single method of demonstration); in that case what we
should have to seek for would be this unique method. But if there is no such
single and general method for solving the question of essence, our task becomes
still more difficult; in the case of each different subject we shall have to
determine the appropriate process of investigation. If to this there be a clear
answer, e.g. that the process is demonstration or division, or some known
method, difficulties and hesitations still beset us-with what facts shall we
begin the inquiry? For the facts which form the starting-points in different
subjects must be different, as e.g. in the case of numbers and surfaces.

First, no doubt, it is necessary to determine in which of
the summa genera soul lies, what it is; is it 'a this-somewhat, 'a substance, or
is it a quale or a quantum, or some other of the remaining kinds of predicates
which we have distinguished? Further, does soul belong to the class of potential
existents, or is it not rather an actuality? Our answer to this question is of
the greatest importance.

We must consider also whether soul is divisible or is
without parts, and whether it is everywhere homogeneous or not; and if not
homogeneous, whether its various forms are different specifically or
generically: up to the present time those who have discussed and investigated
soul seem to have confined themselves to the human soul. We must be careful not
to ignore the question whether soul can be defined in a single unambiguous
formula, as is the case with animal, or whether we must not give a separate
formula for each of it, as we do for horse, dog, man, god (in the latter case
the 'universal' animal-and so too every other 'common predicate'-being treated
either as nothing at all or as a later product). Further, if what exists is not
a plurality of souls, but a plurality of parts of one soul, which ought we to
investigate first, the whole soul or its parts? (It is also a difficult problem
to decide which of these parts are in nature distinct from one another.) Again,
which ought we to investigate first, these parts or their functions, mind or
thinking, the faculty or the act of sensation, and so on? If the investigation
of the functions precedes that of the parts, the further question suggests
itself: ought we not before either to consider the correlative objects, e.g. of
sense or thought? It seems not only useful for the discovery of the causes of
the derived properties of substances to be acquainted with the essential nature
of those substances (as in mathematics it is useful for the understanding of the
property of the equality of the interior angles of a triangle to two right
angles to know the essential nature of the straight and the curved or of the
line and the plane) but also conversely, for the knowledge of the essential
nature of a substance is largely promoted by an acquaintance with its
properties: for, when we are able to give an account conformable to experience
of all or most of the properties of a substance, we shall be in the most
favourable position to say something worth saying about the essential nature of
that subject; in all demonstration a definition of the essence is required as a
starting-point, so that definitions which do not enable us to discover the
derived properties, or which fail to facilitate even a conjecture about them,
must obviously, one and all, be dialectical and futile.

A further problem presented by the affections of soul is
this: are they all affections of the complex of body and soul, or is there any
one among them peculiar to the soul by itself? To determine this is
indispensable but difficult. If we consider the majority of them, there seems to
be no case in which the soul can act or be acted upon without involving the
body; e.g. anger, courage, appetite, and sensation generally. Thinking seems the
most probable exception; but if this too proves to be a form of imagination or
to be impossible without imagination, it too requires a body as a condition of
its existence. If there is any way of acting or being acted upon proper to soul,
soul will be capable of separate existence; if there is none, its separate
existence is impossible. In the latter case, it will be like what is straight,
which has many properties arising from the straightness in it, e.g. that of
touching a bronze sphere at a point, though straightness divorced from the other
constituents of the straight thing cannot touch it in this way; it cannot be so
divorced at all, since it is always found in a body. It therefore seems that all
the affections of soul involve a body-passion, gentleness, fear, pity, courage,
joy, loving, and hating; in all these there is a concurrent affection of the
body. In support of this we may point to the fact that, while sometimes on the
occasion of violent and striking occurrences there is no excitement or fear
felt, on others faint and feeble stimulations produce these emotions, viz. when
the body is already in a state of tension resembling its condition when we are
angry. Here is a still clearer case: in the absence of any external cause of
terror we find ourselves experiencing the feelings of a man in terror. From all
this it is obvious that the affections of soul are enmattered formulable
essences.

Consequently their definitions ought to correspond, e.g.
anger should be defined as a certain mode of movement of such and such a body
(or part or faculty of a body) by this or that cause and for this or that end.
That is precisely why the study of the soul must fall within the science of
Nature, at least so far as in its affections it manifests this double character.
Hence a physicist would define an affection of soul differently from a
dialectician; the latter would define e.g. anger as the appetite for returning
pain for pain, or something like that, while the former would define it as a
boiling of the blood or warm substance surround the heart. The latter assigns
the material conditions, the former the form or formulable essence; for what he
states is the formulable essence of the fact, though for its actual existence
there must be embodiment of it in a material such as is described by the other.
Thus the essence of a house is assigned in such a formula as 'a shelter against
destruction by wind, rain, and heat'; the physicist would describe it as
'stones, bricks, and timbers'; but there is a third possible description which
would say that it was that form in that material with that purpose or end.
Which, then, among these is entitled to be regarded as the genuine physicist?
The one who confines himself to the material, or the one who restricts himself
to the formulable essence alone? Is it not rather the one who combines both in a
single formula? If this is so, how are we to characterize the other two? Must we
not say that there is no type of thinker who concerns himself with those
qualities or attributes of the material which are in fact inseparable from the
material, and without attempting even in thought to separate them? The physicist
is he who concerns himself with all the properties active and passive of bodies
or materials thus or thus defined; attributes not considered as being of this
character he leaves to others, in certain cases it may be to a specialist, e.g.
a carpenter or a physician, in others (a) where they are inseparable in fact,
but are separable from any particular kind of body by an effort of abstraction,
to the mathematician, (b) where they are separate both in fact and in thought
from body altogether, to the First Philosopher or metaphysician. But we must
return from this digression, and repeat that the affections of soul are
inseparable from the material substratum of animal life, to which we have seen
that such affections, e.g. passion and fear, attach, and have not the same mode
of being as a line or a plane.

2

For our study of soul it is necessary, while formulating
the problems of which in our further advance we are to find the solutions, to
call into council the views of those of our predecessors who have declared any
opinion on this subject, in order that we may profit by whatever is sound in
their suggestions and avoid their errors.

The starting-point of our inquiry is an exposition of those
characteristics which have chiefly been held to belong to soul in its very
nature. Two characteristic marks have above all others been recognized as
distinguishing that which has soul in it from that which has not-movement and
sensation. It may be said that these two are what our predecessors have fixed
upon as characteristic of soul.

Some say that what originates movement is both
pre-eminently and primarily soul; believing that what is not itself moved cannot
originate movement in another, they arrived at the view that soul belongs to the
class of things in movement. This is what led Democritus to say that soul is a
sort of fire or hot substance; his 'forms' or atoms are infinite in number;
those which are spherical he calls fire and soul, and compares them to the motes
in the air which we see in shafts of light coming through windows; the mixture
of seeds of all sorts he calls the elements of the whole of Nature (Leucippus
gives a similar account); the spherical atoms are identified with soul because
atoms of that shape are most adapted to permeate everywhere, and to set all the
others moving by being themselves in movement. This implies the view that soul
is identical with what produces movement in animals. That is why, further, they
regard respiration as the characteristic mark of life; as the environment
compresses the bodies of animals, and tends to extrude those atoms which impart
movement to them, because they themselves are never at rest, there must be a
reinforcement of these by similar atoms coming in from without in the act of
respiration; for they prevent the extrusion of those which are already within by
counteracting the compressing and consolidating force of the environment; and
animals continue to live only so long as they are able to maintain this
resistance.

The doctrine of the Pythagoreans seems to rest upon the
same ideas; some of them declared the motes in air, others what moved them, to
be soul. These motes were referred to because they are seen always in movement,
even in a complete calm.

The same tendency is shown by those who define soul as that
which moves itself; all seem to hold the view that movement is what is closest
to the nature of soul, and that while all else is moved by soul, it alone moves
itself. This belief arises from their never seeing anything originating movement
which is not first itself moved.

Similarly also Anaxagoras (and whoever agrees with him in
saying that mind set the whole in movement) declares the moving cause of things
to be soul. His position must, however, be distinguished from that of Democritus.
Democritus roundly identifies soul and mind, for he identifies what appears with
what is true-that is why he commends Homer for the phrase 'Hector lay with
thought distraught'; he does not employ mind as a special faculty dealing with
truth, but identifies soul and mind. What Anaxagoras says about them is more
obscure; in many places he tells us that the cause of beauty and order is mind,
elsewhere that it is soul; it is found, he says, in all animals, great and
small, high and low, but mind (in the sense of intelligence) appears not to
belong alike to all animals, and indeed not even to all human beings.

All those, then, who had special regard to the fact that
what has soul in it is moved, adopted the view that soul is to be identified
with what is eminently originative of movement. All, on the other hand, who
looked to the fact that what has soul in it knows or perceives what is, identify
soul with the principle or principles of Nature, according as they admit several
such principles or one only. Thus Empedocles declares that it is formed out of
all his elements, each of them also being soul; his words are:

For 'tis by Earth we see Earth, by Water Water,

By Ether Ether divine, by Fire destructive Fire,

By Love Love, and Hate by cruel Hate.

In the same way Plato in the Timaeus fashions soul out of
his elements; for like, he holds, is known by like, and things are formed out of
the principles or elements, so that soul must be so too. Similarly also in his
lectures 'On Philosophy' it was set forth that the Animal-itself is compounded
of the Idea itself of the One together with the primary length, breadth, and
depth, everything else, the objects of its perception, being similarly
constituted. Again he puts his view in yet other terms: Mind is the monad,
science or knowledge the dyad (because it goes undeviatingly from one point to
another), opinion the number of the plane, sensation the number of the solid;
the numbers are by him expressly identified with the Forms themselves or
principles, and are formed out of the elements; now things are apprehended
either by mind or science or opinion or sensation, and these same numbers are
the Forms of things.

Some thinkers, accepting both premisses, viz. that the soul
is both originative of movement and cognitive, have compounded it of both and
declared the soul to be a self-moving number.

As to the nature and number of the first principles
opinions differ. The difference is greatest between those who regard them as
corporeal and those who regard them as incorporeal, and from both dissent those
who make a blend and draw their principles from both sources. The number of
principles is also in dispute; some admit one only, others assert several. There
is a consequent diversity in their several accounts of soul; they assume,
naturally enough, that what is in its own nature originative of movement must be
among what is primordial. That has led some to regard it as fire, for fire is
the subtlest of the elements and nearest to incorporeality; further, in the most
primary sense, fire both is moved and originates movement in all the others.

Democritus has expressed himself more ingeniously than the
rest on the grounds for ascribing each of these two characters to soul; soul and
mind are, he says, one and the same thing, and this thing must be one of the
primary and indivisible bodies, and its power of originating movement must be
due to its fineness of grain and the shape of its atoms; he says that of all the
shapes the spherical is the most mobile, and that this is the shape of the
particles of fire and mind.

Anaxagoras, as we said above, seems to distinguish between
soul and mind, but in practice he treats them as a single substance, except that
it is mind that he specially posits as the principle of all things; at any rate
what he says is that mind alone of all that is simple, unmixed, and pure. He
assigns both characteristics, knowing and origination of movement, to the same
principle, when he says that it was mind that set the whole in movement.

Thales, too, to judge from what is recorded about him,
seems to have held soul to be a motive force, since he said that the magnet has
a soul in it because it moves the iron.

Diogenes (and others) held the soul to be air because he
believed air to be finest in grain and a first principle; therein lay the
grounds of the soul's powers of knowing and originating movement. As the
primordial principle from which all other things are derived, it is cognitive;
as finest in grain, it has the power to originate movement.

Heraclitus too says that the first principle-the 'warm
exhalation' of which, according to him, everything else is composed-is soul;
further, that this exhalation is most incorporeal and in ceaseless flux; that
what is in movement requires that what knows it should be in movement; and that
all that is has its being essentially in movement (herein agreeing with the
majority).

Alcmaeon also seems to have held a similar view about soul;
he says that it is immortal because it resembles 'the immortals,' and that this
immortality belongs to it in virtue of its ceaseless movement; for all the
'things divine,' moon, sun, the planets, and the whole heavens, are in perpetual
movement.

of More superficial writers, some, e.g. Hippo, have
pronounced it to be water; they seem to have argued from the fact that the seed
of all animals is fluid, for Hippo tries to refute those who say that the soul
is blood, on the ground that the seed, which is the primordial soul, is not
blood.

Another group (Critias, for example) did hold it to be
blood; they take perception to be the most characteristic attribute of soul, and
hold that perceptiveness is due to the nature of blood.

Each of the elements has thus found its partisan, except
earth-earth has found no supporter unless we count as such those who have
declared soul to be, or to be compounded of, all the elements. All, then, it may
be said, characterize the soul by three marks, Movement, Sensation,
Incorporeality, and each of these is traced back to the first principles. That
is why (with one exception) all those who define the soul by its power of
knowing make it either an element or constructed out of the elements. The
language they all use is similar; like, they say, is known by like; as the soul
knows everything, they construct it out of all the principles. Hence all those
who admit but one cause or element, make the soul also one (e.g. fire or air),
while those who admit a multiplicity of principles make the soul also multiple.
The exception is Anaxagoras; he alone says that mind is impassible and has
nothing in common with anything else. But, if this is so, how or in virtue of
what cause can it know? That Anaxagoras has not explained, nor can any answer be
inferred from his words. All who acknowledge pairs of opposites among their
principles, construct the soul also out of these contraries, while those who
admit as principles only one contrary of each pair, e.g. either hot or cold,
likewise make the soul some one of these. That is why, also, they allow
themselves to be guided by the names; those who identify soul with the hot argue
that sen (to live) is derived from sein (to boil), while those who identify it
with the cold say that soul (psuche) is so called from the process of
respiration and (katapsuxis). Such are the traditional opinions concerning soul,
together with the grounds on which they are maintained.

3

We must begin our examination with movement; for doubtless,
not only is it false that the essence of soul is correctly described by those
who say that it is what moves (or is capable of moving) itself, but it is an
impossibility that movement should be even an attribute of it.

We have already pointed out that there is no necessity that
what originates movement should itself be moved. There are two senses in which
anything may be moved-either (a) indirectly, owing to something other than
itself, or (b) directly, owing to itself. Things are 'indirectly moved' which
are moved as being contained in something which is moved, e.g. sailors in a
ship, for they are moved in a different sense from that in which the ship is
moved; the ship is 'directly moved', they are 'indirectly moved', because they
are in a moving vessel. This is clear if we consider their limbs; the movement
proper to the legs (and so to man) is walking, and in this case the sailors tare
not walking. Recognizing the double sense of 'being moved', what we have to
consider now is whether the soul is 'directly moved' and participates in such
direct movement.

There are four species of movement-locomotion, alteration,
diminution, growth; consequently if the soul is moved, it must be moved with one
or several or all of these species of movement. Now if its movement is not
incidental, there must be a movement natural to it, and, if so, as all the
species enumerated involve place, place must be natural to it. But if the
essence of soul be to move itself, its being moved cannot be incidental to-as it
is to what is white or three cubits long; they too can be moved, but only
incidentally-what is moved is that of which 'white' and 'three cubits long' are
the attributes, the body in which they inhere; hence they have no place: but if
the soul naturally partakes in movement, it follows that it must have a place.

Further, if there be a movement natural to the soul, there
must be a counter-movement unnatural to it, and conversely. The same applies to
rest as well as to movement; for the terminus ad quem of a thing's natural
movement is the place of its natural rest, and similarly the terminus ad quem of
its enforced movement is the place of its enforced rest. But what meaning can be
attached to enforced movements or rests of the soul, it is difficult even to
imagine.

Further, if the natural movement of the soul be upward, the
soul must be fire; if downward, it must be earth; for upward and downward
movements are the definitory characteristics of these bodies. The same reasoning
applies to the intermediate movements, termini, and bodies. Further, since the
soul is observed to originate movement in the body, it is reasonable to suppose
that it transmits to the body the movements by which it itself is moved, and so,
reversing the order, we may infer from the movements of the body back to similar
movements of the soul. Now the body is moved from place to place with movements
of locomotion. Hence it would follow that the soul too must in accordance with
the body change either its place as a whole or the relative places of its parts.
This carries with it the possibility that the soul might even quit its body and
re-enter it, and with this would be involved the possibility of a resurrection
of animals from the dead. But, it may be contended, the soul can be moved
indirectly by something else; for an animal can be pushed out of its course.
Yes, but that to whose essence belongs the power of being moved by itself,
cannot be moved by something else except incidentally, just as what is good by
or in itself cannot owe its goodness to something external to it or to some end
to which it is a means.

If the soul is moved, the most probable view is that what
moves it is sensible things.

We must note also that, if the soul moves itself, it must
be the mover itself that is moved, so that it follows that if movement is in
every case a displacement of that which is in movement, in that respect in which
it is said to be moved, the movement of the soul must be a departure from its
essential nature, at least if its self-movement is essential to it, not
incidental.

Some go so far as to hold that the movements which the soul
imparts to the body in which it is are the same in kind as those with which it
itself is moved. An example of this is Democritus, who uses language like that
of the comic dramatist Philippus, who accounts for the movements that Daedalus
imparted to his wooden Aphrodite by saying that he poured quicksilver into it;
similarly Democritus says that the spherical atoms which according to him
constitute soul, owing to their own ceaseless movements draw the whole body
after them and so produce its movements. We must urge the question whether it is
these very same atoms which produce rest also-how they could do so, it is
difficult and even impossible to say. And, in general, we may object that it is
not in this way that the soul appears to originate movement in animals-it is
through intention or process of thinking.

It is in the same fashion that the Timaeus also tries to
give a physical account of how the soul moves its body; the soul, it is there
said, is in movement, and so owing to their mutual implication moves the body
also. After compounding the soul-substance out of the elements and dividing it
in accordance with the harmonic numbers, in order that it may possess a connate
sensibility for 'harmony' and that the whole may move in movements well attuned,
the Demiurge bent the straight line into a circle; this single circle he divided
into two circles united at two common points; one of these he subdivided into
seven circles. All this implies that the movements of the soul are identified
with the local movements of the heavens.

Now, in the
first place, it is a mistake to say that the soul is a spatial magnitude. It is
evident that Plato means the soul of the whole to be like the sort of soul which
is called mind not like the sensitive or the desiderative soul, for the
movements of neither of these are circular. Now mind is one and continuous in
the sense in which the process of thinking is so, and thinking is identical with
the thoughts which are its parts; these have a serial unity like that of number,
not a unity like that of a spatial magnitude. Hence mind cannot have that kind
of unity either; mind is either without parts or is continuous in some other way
than that which characterizes a spatial magnitude. How, indeed, if it were a
spatial magnitude, could mind possibly think? Will it think with any one
indifferently of its parts? In this case, the 'part' must be understood either
in the sense of a spatial magnitude or in the sense of a point (if a point can
be called a part of a spatial magnitude). If we accept the latter alternative,
the points being infinite in number, obviously the mind can never exhaustively
traverse them; if the former, the mind must think the same thing over and over
again, indeed an infinite number of times (whereas it is manifestly possible to
think a thing once only). If contact of any part whatsoever of itself with the
object is all that is required, why need mind move in a circle, or indeed
possess magnitude at all? On the other hand, if contact with the whole circle is
necessary, what meaning can be given to the contact of the parts? Further, how
could what has no parts think what has parts, or what has parts think what has
none? We must identify the circle referred to with mind; for it is mind whose
movement is thinking, and it is the circle whose movement is revolution, so that
if thinking is a movement of revolution, the circle which has this
characteristic movement must be mind.

If the circular movement is eternal, there must be
something which mind is always thinking-what can this be? For all practical
processes of thinking have limits-they all go on for the sake of something
outside the process, and all theoretical processes come to a close in the same
way as the phrases in speech which express processes and results of thinking.
Every such linguistic phrase is either definitory or demonstrative.
Demonstration has both a starting-point and may be said to end in a conclusion
or inferred result; even if the process never reaches final completion, at any
rate it never returns upon itself again to its starting-point, it goes on
assuming a fresh middle term or a fresh extreme, and moves straight forward, but
circular movement returns to its starting-point. Definitions, too, are closed
groups of terms.

Further, if the same revolution is repeated, mind must
repeatedly think the same object.

Further, thinking has more resemblance to a coming to rest
or arrest than to a movement; the same may be said of inferring.

It might also be urged that what is difficult and enforced
is incompatible with blessedness; if the movement of the soul is not of its
essence, movement of the soul must be contrary to its nature. It must also be
painful for the soul to be inextricably bound up with the body; nay more, if, as
is frequently said and widely accepted, it is better for mind not to be
embodied, the union must be for it undesirable.

Further, the cause of the revolution of the heavens is left
obscure. It is not the essence of soul which is the cause of this circular
movement-that movement is only incidental to soul-nor is, a fortiori, the body
its cause. Again, it is not even asserted that it is better that soul should be
so moved; and yet the reason for which God caused the soul to move in a circle
can only have been that movement was better for it than rest, and movement of
this kind better than any other. But since this sort of consideration is more
appropriate to another field of speculation, let us dismiss it for the present.

The view we have just been examining, in company with most
theories about the soul, involves the following absurdity: they all join the
soul to a body, or place it in a body, without adding any specification of the
reason of their union, or of the bodily conditions required for it. Yet such
explanation can scarcely be omitted; for some community of nature is presupposed
by the fact that the one acts and the other is acted upon, the one moves and the
other is moved; interaction always implies a special nature in the two
interagents. All, however, that these thinkers do is to describe the specific
characteristics of the soul; they do not try to determine anything about the
body which is to contain it, as if it were possible, as in the Pythagorean
myths, that any soul could be clothed upon with any body-an absurd view, for
each body seems to have a form and shape of its own. It is as absurd as to say
that the art of carpentry could embody itself in flutes; each art must use its
tools, each soul its body.

4

There is yet another theory about soul, which has commended
itself to many as no less probable than any of those we have hitherto mentioned,
and has rendered public account of itself in the court of popular discussion.
Its supporters say that the soul is a kind of harmony, for (a) harmony is a
blend or composition of contraries, and (b) the body is compounded out of
contraries. Harmony, however, is a certain proportion or composition of the
constituents blended, and soul can be neither the one nor the other of these.
Further, the power of originating movement cannot belong to a harmony, while
almost all concur in regarding this as a principal attribute of soul. It is more
appropriate to call health (or generally one of the good states of the body) a
harmony than to predicate it of the soul. The absurdity becomes most apparent
when we try to attribute the active and passive affections of the soul to a
harmony; the necessary readjustment of their conceptions is difficult. Further,
in using the word 'harmony' we have one or other of two cases in our mind; the
most proper sense is in relation to spatial magnitudes which have motion and
position, where harmony means the disposition and cohesion of their parts in
such a manner as to prevent the introduction into the whole of anything
homogeneous with it, and the secondary sense, derived from the former, is that
in which it means the ratio between the constituents so blended; in neither of
these senses is it plausible to predicate it of soul. That soul is a harmony in
the sense of the mode of composition of the parts of the body is a view easily
refutable; for there are many composite parts and those variously compounded; of
what bodily part is mind or the sensitive or the appetitive faculty the mode of
composition? And what is the mode of composition which constitutes each of them?
It is equally absurd to identify the soul with the ratio of the mixture; for the
mixture which makes flesh has a different ratio between the elements from that
which makes bone. The consequence of this view will therefore be that
distributed throughout the whole body there will be many souls, since every one
of the bodily parts is a different mixture of the elements, and the ratio of
mixture is in each case a harmony, i.e. a soul.

From Empedocles at any rate we might demand an answer to
the following question for he says that each of the parts of the body is what it
is in virtue of a ratio between the elements: is the soul identical with this
ratio, or is it not rather something over and above this which is formed in the
parts? Is love the cause of any and every mixture, or only of those that are in
the right ratio? Is love this ratio itself, or is love something over and above
this? Such are the problems raised by this account. But, on the other hand, if
the soul is different from the mixture, why does it disappear at one and the
same moment with that relation between the elements which constitutes flesh or
the other parts of the animal body? Further, if the soul is not identical with
the ratio of mixture, and it is consequently not the case that each of the parts
has a soul, what is that which perishes when the soul quits the body?

That the soul cannot either be a harmony, or be moved in a
circle, is clear from what we have said. Yet that it can be moved incidentally
is, as we said above, possible, and even that in a sense it can move itself,
i.e. in the sense that the vehicle in which it is can be moved, and moved by it;
in no other sense can the soul be moved in space.

More legitimate doubts might remain as to its movement in
view of the following facts. We speak of the soul as being pained or pleased,
being bold or fearful, being angry, perceiving, thinking. All these are regarded
as modes of movement, and hence it might be inferred that the soul is moved.
This, however, does not necessarily follow. We may admit to the full that being
pained or pleased, or thinking, are movements (each of them a 'being moved'),
and that the movement is originated by the soul. For example we may regard anger
or fear as such and such movements of the heart, and thinking as such and such
another movement of that organ, or of some other; these modifications may arise
either from changes of place in certain parts or from qualitative alterations
(the special nature of the parts and the special modes of their changes being
for our present purpose irrelevant). Yet to say that it is the soul which is
angry is as inexact as it would be to say that it is the soul that weaves webs
or builds houses. It is doubtless better to avoid saying that the soul pities or
learns or thinks and rather to say that it is the man who does this with his
soul. What we mean is not that the movement is in the soul, but that sometimes
it terminates in the soul and sometimes starts from it, sensation e.g. coming
from without inwards, and reminiscence starting from the soul and terminating
with the movements, actual or residual, in the sense organs.

The case of mind is different; it seems to be an
independent substance implanted within the soul and to be incapable of being
destroyed. If it could be destroyed at all, it would be under the blunting
influence of old age. What really happens in respect of mind in old age is,
however, exactly parallel to what happens in the case of the sense organs; if
the old man could recover the proper kind of eye, he would see just as well as
the young man. The incapacity of old age is due to an affection not of the soul
but of its vehicle, as occurs in drunkenness or disease. Thus it is that in old
age the activity of mind or intellectual apprehension declines only through the
decay of some other inward part; mind itself is impassible. Thinking, loving,
and hating are affections not of mind, but of that which has mind, so far as it
has it. That is why, when this vehicle decays, memory and love cease; they were
activities not of mind, but of the composite which has perished; mind is, no
doubt, something more divine and impassible. That the soul cannot be moved is
therefore clear from what we have said, and if it cannot be moved at all,
manifestly it cannot be moved by itself.

Of all the opinions we have enumerated, by far the most
unreasonable is that which declares the soul to be a self-moving number; it
involves in the first place all the impossibilities which follow from regarding
the soul as moved, and in the second special absurdities which follow from
calling it a number. How we to imagine a unit being moved? By what agency? What
sort of movement can be attributed to what is without parts or internal
differences? If the unit is both originative of movement and itself capable of
being moved, it must contain difference.

Further, since they say a moving line generates a surface
and a moving point a line, the movements of the psychic units must be lines (for
a point is a unit having position, and the number of the soul is, of course,
somewhere and has position).

Again, if from a number a number or a unit is subtracted,
the remainder is another number; but plants and many animals when divided
continue to live, and each segment is thought to retain the same kind of soul.

It must be all the same whether we speak of units or
corpuscles; for if the spherical atoms of Democritus became points, nothing
being retained but their being a quantum, there must remain in each a moving and
a moved part, just as there is in what is continuous; what happens has nothing
to do with the size of the atoms, it depends solely upon their being a quantum.
That is why there must be something to originate movement in the units. If in
the animal what originates movement is the soul, so also must it be in the case
of the number, so that not the mover and the moved together, but the mover only,
will be the soul. But how is it possible for one of the units to fulfil this
function of originating movement? There must be some difference between such a
unit and all the other units, and what difference can there be between one
placed unit and another except a difference of position? If then, on the other
hand, these psychic units within the body are different from the points of the
body, there will be two sets of units both occupying the same place; for each
unit will occupy a point. And yet, if there can be two, why cannot there be an
infinite number? For if things can occupy an indivisible lace, they must
themselves be indivisible. If, on the other hand, the points of the body are
identical with the units whose number is the soul, or if the number of the
points in the body is the soul, why have not all bodies souls? For all bodies
contain points or an infinity of points.

Further, how is it possible for these points to be isolated
or separated from their bodies, seeing that lines cannot be resolved into
points?

5

The result is, as we have said, that this view, while on
the one side identical with that of those who maintain that soul is a subtle
kind of body, is on the other entangled in the absurdity peculiar to Democritus'
way of describing the manner in which movement is originated by soul. For if the
soul is present throughout the whole percipient body, there must, if the soul be
a kind of body, be two bodies in the same place; and for those who call it a
number, there must be many points at one point, or every body must have a soul,
unless the soul be a different sort of number-other, that is, than the sum of
the points existing in a body. Another consequence that follows is that the
animal must be moved by its number precisely in the way that Democritus
explained its being moved by his spherical psychic atoms. What difference does
it make whether we speak of small spheres or of large units, or, quite simply,
of units in movement? One way or another, the movements of the animal must be
due to their movements. Hence those who combine movement and number in the same
subject lay themselves open to these and many other similar absurdities. It is
impossible not only that these characters should give the definition of soul-it
is impossible that they should even be attributes of it. The point is clear if
the attempt be made to start from this as the account of soul and explain from
it the affections and actions of the soul, e.g. reasoning, sensation, pleasure,
pain, &c. For, to repeat what we have said earlier, movement and number do
not facilitate even conjecture about the derivative properties of soul.

Such are the three ways in which soul has traditionally
been defined; one group of thinkers declared it to be that which is most
originative of movement because it moves itself, another group to be the
subtlest and most nearly incorporeal of all kinds of body. We have now
sufficiently set forth the difficulties and inconsistencies to which these
theories are exposed. It remains now to examine the doctrine that soul is
composed of the elements.

The reason assigned for this doctrine is that thus the soul
may perceive or come to know everything that is, but the theory necessarily
involves itself in many impossibilities. Its upholders assume that like is known
only by like, and imagine that by declaring the soul to be composed of the
elements they succeed in identifying the soul with all the things it is capable
of apprehending. But the elements are not the only things it knows; there are
many others, or, more exactly, an infinite number of others, formed out of the
elements. Let us admit that the soul knows or perceives the elements out of
which each of these composites is made up; but by what means will it know or
perceive the composite whole, e.g. what God, man, flesh, bone (or any other
compound) is? For each is, not merely the elements of which it is composed, but
those elements combined in a determinate mode or ratio, as Empedocles himself
says of bone,

The kindly Earth in its broad-bosomed moulds

Won of clear
Water two parts out of eight,

And four of
Fire; and so white bones were formed.

Nothing, therefore, will be gained by the presence of the
elements in the soul, unless there be also present there the various formulae of
proportion and the various compositions in accordance with them. Each element
will indeed know its fellow outside, but there will be no knowledge of bone or
man, unless they too are present in the constitution of the soul. The
impossibility of this needs no pointing out; for who would suggest that stone or
man could enter into the constitution of the soul? The same applies to 'the
good' and 'the not-good', and so on.

Further, the word 'is' has many meanings: it may be used of
a 'this' or substance, or of a quantum, or of a quale, or of any other of the
kinds of predicates we have distinguished. Does the soul consist of all of these
or not? It does not appear that all have common elements. Is the soul formed out
of those elements alone which enter into substances? so how will it be able to
know each of the other kinds of thing? Will it be said that each kind of thing
has elements or principles of its own, and that the soul is formed out of the
whole of these? In that case, the soul must be a quantum and a quale and a
substance. But all that can be made out of the elements of a quantum is a
quantum, not a substance. These (and others like them) are the consequences of
the view that the soul is composed of all the elements.

It is absurd, also, to say both (a) that like is not
capable of being affected by like, and (b) that like is perceived or known by
like, for perceiving, and also both thinking and knowing, are, on their own
assumption, ways of being affected or moved.

There are many puzzles and difficulties raised by saying,
as Empedocles does, that each set of things is known by means of its corporeal
elements and by reference to something in soul which is like them, and
additional testimony is furnished by this new consideration; for all the parts
of the animal body which consist wholly of earth such as bones, sinews, and hair
seem to be wholly insensitive and consequently not perceptive even of objects
earthy like themselves, as they ought to have been.

Further, each of the principles will have far more
ignorance than knowledge, for though each of them will know one thing, there
will be many of which it will be ignorant. Empedocles at any rate must conclude
that his God is the least intelligent of all beings, for of him alone is it true
that there is one thing, Strife, which he does not know, while there is nothing
which mortal beings do not know, for ere is nothing which does not enter into
their composition.

In general, we may ask, Why has not everything a soul,
since everything either is an element, or is formed out of one or several or all
of the elements? Each must certainly know one or several or all.

The problem might also be raised, What is that which
unifies the elements into a soul? The elements correspond, it would appear, to
the matter; what unites them, whatever it is, is the supremely important factor.
But it is impossible that there should be something superior to, and dominant
over, the soul (and a fortiori over the mind); it is reasonable to hold that
mind is by nature most primordial and dominant, while their statement that it is
the elements which are first of all that is.

All, both those who assert that the soul, because of its
knowledge or perception of what is compounded out of the elements, and is those
who assert that it is of all things the most originative of movement, fail to
take into consideration all kinds of soul. In fact (1) not all beings that
perceive can originate movement; there appear to be certain animals which
stationary, and yet local movement is the only one, so it seems, which the soul
originates in animals. And (2) the same object-on holds against all those who
construct mind and the perceptive faculty out of the elements; for it appears
that plants live, and yet are not endowed with locomotion or perception, while a
large number of animals are without discourse of reason. Even if these points
were waived and mind admitted to be a part of the soul (and so too the
perceptive faculty), still, even so, there would be kinds and parts of soul of
which they had failed to give any account.

The same objection lies against the view expressed in the
'Orphic' poems: there it is said that the soul comes in from the whole when
breathing takes place, being borne in upon the winds. Now this cannot take place
in the case of plants, nor indeed in the case of certain classes of animal, for
not all classes of animal breathe. This fact has escaped the notice of the
holders of this view.

If we must construct the soul out of the elements, there is
no necessity to suppose that all the elements enter into its construction; one
element in each pair of contraries will suffice to enable it to know both that
element itself and its contrary. By means of the straight line we know both
itself and the curved-the carpenter's rule enables us to test both-but what is
curved does not enable us to distinguish either itself or the straight. Certain
thinkers say that soul is intermingled in the whole universe, and it is perhaps
for that reason that Thales came to the opinion that all things are full of
gods. This presents some difficulties: Why does the soul when it resides in air
or fire not form an animal, while it does so when it resides in mixtures of the
elements, and that although it is held to be of higher quality when contained in
the former? (One might add the question, why the soul in air is maintained to be
higher and more immortal than that in animals.) Both possible ways of replying
to the former question lead to absurdity or paradox; for it is beyond paradox to
say that fire or air is an animal, and it is absurd to refuse the name of animal
to what has soul in it. The opinion that the elements have soul in them seems to
have arisen from the doctrine that a whole must be homogeneous with its parts.
If it is true that animals become animate by drawing into themselves a portion
of what surrounds them, the partisans of this view are bound to say that the
soul of the Whole too is homogeneous with all its parts. If the air sucked in is
homogeneous, but soul heterogeneous, clearly while some part of soul will exist
in the inbreathed air, some other part will not. The soul must either be
homogeneous, or such that there are some parts of the Whole in which it is not
to be found.

From what has been said it is now clear that knowing as an
attribute of soul cannot be explained by soul's being composed of the elements,
and that it is neither sound nor true to speak of soul as moved. But since (a)
knowing, perceiving, opining, and further (b) desiring, wishing, and generally
all other modes of appetition, belong to soul, and (c) the local movements of
animals, and (d) growth, maturity, and decay are produced by the soul, we must
ask whether each of these is an attribute of the soul as a whole, i.e. whether
it is with the whole soul we think, perceive, move ourselves, act or are acted
upon, or whether each of them requires a different part of the soul? So too with
regard to life. Does it depend on one of the parts of soul? Or is it dependent
on more than one? Or on all? Or has it some quite other cause?

Some hold that the soul is divisible, and that one part
thinks, another desires. If, then, its nature admits of its being divided, what
can it be that holds the parts together? Surely not the body; on the contrary it
seems rather to be the soul that holds the body together; at any rate when the
soul departs the body disintegrates and decays. If, then, there is something
else which makes the soul one, this unifying agency would have the best right to
the name of soul, and we shall have to repeat for it the question: Is it one or
multipartite? If it is one, why not at once admit that 'the soul' is one? If it
has parts, once more the question must be put: What holds its parts together,
and so ad infinitum?

The question might also be raised about the parts of the
soul: What is the separate role of each in relation to the body? For, if the
whole soul holds together the whole body, we should expect each part of the soul
to hold together a part of the body. But this seems an impossibility; it is
difficult even to imagine what sort of bodily part mind will hold together, or
how it will do this.

It is a fact of observation that plants and certain insects
go on living when divided into segments; this means that each of the segments
has a soul in it identical in species, though not numerically identical in the
different segments, for both of the segments for a time possess the power of
sensation and local movement. That this does not last is not surprising, for
they no longer possess the organs necessary for self-maintenance. But, all the
same, in each of the bodily parts there are present all the parts of soul, and
the souls so present are homogeneous with one another and with the whole; this
means that the several parts of the soul are indisseverable from one another,
although the whole soul is divisible. It seems also that the principle found in
plants is also a kind of soul; for this is the only principle which is common to
both animals and plants; and this exists in isolation from the principle of
sensation, though there nothing which has the latter without the former.

Book II

1

LET the foregoing suffice as our account of the views
concerning the soul which have been handed on by our predecessors; let us now
dismiss them and make as it were a completely fresh start, endeavouring to give
a precise answer to the question, What is soul? i.e. to formulate the most
general possible definition of it.

We are in the habit of recognizing, as one determinate kind
of what is, substance, and that in several senses, (a) in the sense of matter or
that which in itself is not 'a this', and (b) in the sense of form or essence,
which is that precisely in virtue of which a thing is called 'a this', and
thirdly (c) in the sense of that which is compounded of both (a) and (b). Now
matter is potentiality, form actuality; of the latter there are two grades
related to one another as e.g. knowledge to the exercise of knowledge.

Among substances are by general consent reckoned bodies and
especially natural bodies; for they are the principles of all other bodies. Of
natural bodies some have life in them, others not; by life we mean
self-nutrition and growth (with its correlative decay). It follows that every
natural body which has life in it is a substance in the sense of a composite.

But since it is also a body of such and such a kind, viz.
having life, the body cannot be soul; the body is the subject or matter, not
what is attributed to it. Hence the soul must be a substance in the sense of the
form of a natural body having life potentially within it. But substance is
actuality, and thus soul is the actuality of a body as above characterized. Now
the word actuality has two senses corresponding respectively to the possession
of knowledge and the actual exercise of knowledge. It is obvious that the soul
is actuality in the first sense, viz. that of knowledge as possessed, for both
sleeping and waking presuppose the existence of soul, and of these waking
corresponds to actual knowing, sleeping to knowledge possessed but not employed,
and, in the history of the individual, knowledge comes before its employment or
exercise.

That is why the soul is the first grade of actuality of a
natural body having life potentially in it. The body so described is a body
which is organized. The parts of plants in spite of their extreme simplicity are
'organs'; e.g. the leaf serves to shelter the pericarp, the pericarp to shelter
the fruit, while the roots of plants are analogous to the mouth of animals, both
serving for the absorption of food. If, then, we have to give a general formula
applicable to all kinds of soul, we must describe it as the first grade of
actuality of a natural organized body. That is why we can wholly dismiss as
unnecessary the question whether the soul and the body are one: it is as
meaningless as to ask whether the wax and the shape given to it by the stamp are
one, or generally the matter of a thing and that of which it is the matter.
Unity has many senses (as many as 'is' has), but the most proper and fundamental
sense of both is the relation of an actuality to that of which it is the
actuality. We have now given an answer to the question, What is soul?-an answer
which applies to it in its full extent. It is substance in the sense which
corresponds to the definitive formula of a thing's essence. That means that it
is 'the essential whatness' of a body of the character just assigned. Suppose
that what is literally an 'organ', like an axe, were a natural body, its
'essential whatness', would have been its essence, and so its soul; if this
disappeared from it, it would have ceased to be an axe, except in name. As it
is, it is just an axe; it wants the character which is required to make its
whatness or formulable essence a soul; for that, it would have had to be a
natural body of a particular kind, viz. one having in itself the power of
setting itself in movement and arresting itself. Next, apply this doctrine in
the case of the 'parts' of the living body. Suppose that the eye were an
animal-sight would have been its soul, for sight is the substance or essence of
the eye which corresponds to the formula, the eye being merely the matter of
seeing; when seeing is removed the eye is no longer an eye, except in name-it is
no more a real eye than the eye of a statue or of a painted figure. We must now
extend our consideration from the 'parts' to the whole living body; for what the
departmental sense is to the bodily part which is its organ, that the whole
faculty of sense is to the whole sensitive body as such.

We must not understand by that which is 'potentially
capable of living' what has lost the soul it had, but only what still retains
it; but seeds and fruits are bodies which possess the qualification.
Consequently, while waking is actuality in a sense corresponding to the cutting
and the seeing, the soul is actuality in the sense corresponding to the power of
sight and the power in the tool; the body corresponds to what exists in
potentiality; as the pupil plus the power of sight constitutes the eye, so the
soul plus the body constitutes the animal.

From this it indubitably follows that the soul is
inseparable from its body, or at any rate that certain parts of it are (if it
has parts) for the actuality of some of them is nothing but the actualities of
their bodily parts. Yet some may be separable because they are not the
actualities of any body at all. Further, we have no light on the problem whether
the soul may not be the actuality of its body in the sense in which the sailor
is the actuality of the ship.

This must suffice as our sketch or outline determination of
the nature of soul.

2

Since what is clear or logically more evident emerges from
what in itself is confused but more observable by us, we must reconsider our
results from this point of view. For it is not enough for a definitive formula
to express as most now do the mere fact; it must include and exhibit the ground
also. At present definitions are given in a form analogous to the conclusion of
a syllogism; e.g. What is squaring? The construction of an equilateral rectangle
equal to a given oblong rectangle. Such a definition is in form equivalent to a
conclusion. One that tells us that squaring is the discovery of a line which is
a mean proportional between the two unequal sides of the given rectangle
discloses the ground of what is defined.

We resume our inquiry from a fresh starting-point by
calling attention to the fact that what has soul in it differs from what has
not, in that the former displays life. Now this word has more than one sense,
and provided any one alone of these is found in a thing we say that thing is
living. Living, that is, may mean thinking or perception or local movement and
rest, or movement in the sense of nutrition, decay and growth. Hence we think of
plants also as living, for they are observed to possess in themselves an
originative power through which they increase or decrease in all spatial
directions; they grow up and down, and everything that grows increases its bulk
alike in both directions or indeed in all, and continues to live so long as it
can absorb nutriment.

This power of self-nutrition can be isolated from the other
powers mentioned, but not they from it-in mortal beings at least. The fact is
obvious in plants; for it is the only psychic power they possess.

This is the originative power the possession of which leads
us to speak of things as living at all, but it is the possession of sensation
that leads us for the first time to speak of living things as animals; for even
those beings which possess no power of local movement but do possess the power
of sensation we call animals and not merely living things.

The primary form of sense is touch, which belongs to all
animals. just as the power of self-nutrition can be isolated from touch and
sensation generally, so touch can be isolated from all other forms of sense. (By
the power of self-nutrition we mean that departmental power of the soul which is
common to plants and animals: all animals whatsoever are observed to have the
sense of touch.) What the explanation of these two facts is, we must discuss
later. At present we must confine ourselves to saying that soul is the source of
these phenomena and is characterized by them, viz. by the powers of
self-nutrition, sensation, thinking, and motivity.

Is each of these a soul or a part of a soul? And if a part,
a part in what sense? A part merely distinguishable by definition or a part
distinct in local situation as well? In the case of certain of these powers, the
answers to these questions are easy, in the case of others we are puzzled what
to say. just as in the case of plants which when divided are observed to
continue to live though removed to a distance from one another (thus showing
that in their case the soul of each individual plant before division was
actually one, potentially many), so we notice a similar result in other
varieties of soul, i.e. in insects which have been cut in two; each of the
segments possesses both sensation and local movement; and if sensation,
necessarily also imagination and appetition; for, where there is sensation,
there is also pleasure and pain, and, where these, necessarily also desire.

We have no evidence as yet about mind or the power to
think; it seems to be a widely different kind of soul, differing as what is
eternal from what is perishable; it alone is capable of existence in isolation
from all other psychic powers. All the other parts of soul, it is evident from
what we have said, are, in spite of certain statements to the contrary,
incapable of separate existence though, of course, distinguishable by
definition. If opining is distinct from perceiving, to be capable of opining and
to be capable of perceiving must be distinct, and so with all the other forms of
living above enumerated. Further, some animals possess all these parts of soul,
some certain of them only, others one only (this is what enables us to classify
animals); the cause must be considered later.' A similar arrangement is found
also within the field of the senses; some classes of animals have all the
senses, some only certain of them, others only one, the most indispensable,
touch.

Since the expression 'that whereby we live and perceive'
has two meanings, just like the expression 'that whereby we know'-that may mean
either (a) knowledge or (b) the soul, for we can speak of knowing by or with
either, and similarly that whereby we are in health may be either (a) health or
(b) the body or some part of the body; and since of the two terms thus
contrasted knowledge or health is the name of a form, essence, or ratio, or if
we so express it an actuality of a recipient matter-knowledge of what is capable
of knowing, health of what is capable of being made healthy (for the operation
of that which is capable of originating change terminates and has its seat in
what is changed or altered); further, since it is the soul by or with which
primarily we live, perceive, and think:-it follows that the soul must be a ratio
or formulable essence, not a matter or subject. For, as we said, word substance
has three meanings form, matter, and the complex of both and of these three what
is called matter is potentiality, what is called form actuality. Since then the
complex here is the living thing, the body cannot be the actuality of the soul;
it is the soul which is the actuality of a certain kind of body. Hence the
rightness of the view that the soul cannot be without a body, while it csnnot he
a body; it is not a body but something relative to a body. That is why it is in
a body, and a body of a definite kind. It was a mistake, therefore, to do as
former thinkers did, merely to fit it into a body without adding a definite
specification of the kind or character of that body. Reflection confirms the
observed fact; the actuality of any given thing can only be realized in what is
already potentially that thing, i.e. in a matter of its own appropriate to it.
From all this it follows that soul is an actuality or formulable essence of
something that possesses a potentiality of being besouled.

3

Of the psychic powers above enumerated some kinds of living
things, as we have said, possess all, some less than all, others one only. Those
we have mentioned are the nutritive, the appetitive, the sensory, the
locomotive, and the power of thinking. Plants have none but the first, the
nutritive, while another order of living things has this plus the sensory. If
any order of living things has the sensory, it must also have the appetitive;
for appetite is the genus of which desire, passion, and wish are the species;
now all animals have one sense at least, viz. touch, and whatever has a sense
has the capacity for pleasure and pain and therefore has pleasant and painful
objects present to it, and wherever these are present, there is desire, for
desire is just appetition of what is pleasant. Further, all animals have the
sense for food (for touch is the sense for food); the food of all living things
consists of what is dry, moist, hot, cold, and these are the qualities
apprehended by touch; all other sensible qualities are apprehended by touch only
indirectly. Sounds, colours, and odours contribute nothing to nutriment;
flavours fall within the field of tangible qualities. Hunger and thirst are
forms of desire, hunger a desire for what is dry and hot, thirst a desire for
what is cold and moist; flavour is a sort of seasoning added to both. We must
later clear up these points, but at present it may be enough to say that all
animals that possess the sense of touch have also appetition. The case of
imagination is obscure; we must examine it later. Certain kinds of animals
possess in addition the power of locomotion, and still another order of animate
beings, i.e. man and possibly another order like man or superior to him, the
power of thinking, i.e. mind. It is now evident that a single definition can be
given of soul only in the same sense as one can be given of figure. For, as in
that case there is no figure distinguishable and apart from triangle, &c.,
so here there is no soul apart from the forms of soul just enumerated. It is
true that a highly general definition can be given for figure which will fit all
figures without expressing the peculiar nature of any figure. So here in the
case of soul and its specific forms. Hence it is absurd in this and similar
cases to demand an absolutely general definition which will fail to express the
peculiar nature of anything that is, or again, omitting this, to look for
separate definitions corresponding to each infima species. The cases of figure
and soul are exactly parallel; for the particulars subsumed under the common
name in both cases-figures and living beings-constitute a series, each
successive term of which potentially contains its predecessor, e.g. the square
the triangle, the sensory power the self-nutritive. Hence we must ask in the
case of each order of living things, What is its soul, i.e. What is the soul of
plant, animal, man? Why the terms are related in this serial way must form the
subject of later examination. But the facts are that the power of perception is
never found apart from the power of self-nutrition, while-in plants-the latter
is found isolated from the former. Again, no sense is found apart from that of
touch, while touch is found by itself; many animals have neither sight, hearing,
nor smell. Again, among living things that possess sense some have the power of
locomotion, some not. Lastly, certain living beings-a small minority-possess
calculation and thought, for (among mortal beings) those which possess
calculation have all the other powers above mentioned, while the converse does
not hold-indeed some live by imagination alone, while others have not even
imagination. The mind that knows with immediate intuition presents a different
problem.

It is evident that the way to give the most adequate
definition of soul is to seek in the case of each of its forms for the most
appropriate definition.

4

It is necessary for the student of these forms of soul
first to find a definition of each, expressive of what it is, and then to
investigate its derivative properties, &c. But if we are to express what
each is, viz. what the thinking power is, or the perceptive, or the nutritive,
we must go farther back and first give an account of thinking or perceiving, for
in the order of investigation the question of what an agent does precedes the
question, what enables it to do what it does. If this is correct, we must on the
same ground go yet another step farther back and have some clear view of the
objects of each; thus we must start with these objects, e.g. with food, with
what is perceptible, or with what is intelligible.

It follows that first of all we must treat of nutrition and
reproduction, for the nutritive soul is found along with all the others and is
the most primitive and widely distributed power of soul, being indeed that one
in virtue of which all are said to have life. The acts in which it manifests
itself are reproduction and the use of food-reproduction, I say, because for any
living thing that has reached its normal development and which is unmutilated,
and whose mode of generation is not spontaneous, the most natural act is the
production of another like itself, an animal producing an animal, a plant a
plant, in order that, as far as its nature allows, it may partake in the eternal
and divine. That is the goal towards which all things strive, that for the sake
of which they do whatsoever their nature renders possible. The phrase 'for the
sake of which' is ambiguous; it may mean either (a) the end to achieve which, or
(b) the being in whose interest, the act is done. Since then no living thing is
able to partake in what is eternal and divine by uninterrupted continuance (for
nothing perishable can for ever remain one and the same), it tries to achieve
that end in the only way possible to it, and success is possible in varying
degrees; so it remains not indeed as the self-same individual but continues its
existence in something like itself-not numerically but specifically one.

The soul is the cause or source of the living body. The
terms cause and source have many senses. But the soul is the cause of its body
alike in all three senses which we explicitly recognize. It is (a) the source or
origin of movement, it is (b) the end, it is (c) the essence of the whole living
body.

That it is the last, is clear; for in everything the
essence is identical with the ground of its being, and here, in the case of
living things, their being is to live, and of their being and their living the
soul in them is the cause or source. Further, the actuality of whatever is
potential is identical with its formulable essence.

It is manifest that the soul is also the final cause of its
body. For Nature, like mind, always does whatever it does for the sake of
something, which something is its end. To that something corresponds in the case
of animals the soul and in this it follows the order of nature; all natural
bodies are organs of the soul. This is true of those that enter into the
constitution of plants as well as of those which enter into that of animals.
This shows that that the sake of which they are is soul. We must here recall the
two senses of 'that for the sake of which', viz. (a) the end to achieve which,
and (b) the being in whose interest, anything is or is done.

We must maintain, further, that the soul is also the cause
of the living body as the original source of local movement. The power of
locomotion is not found, however, in all living things. But change of quality
and change of quantity are also due to the soul. Sensation is held to be a
qualitative alteration, and nothing except what has soul in it is capable of
sensation. The same holds of the quantitative changes which constitute growth
and decay; nothing grows or decays naturally except what feeds itself, and
nothing feeds itself except what has a share of soul in it.

Empedocles is wrong in adding that growth in plants is to
be explained, the downward rooting by the natural tendency of earth to travel
downwards, and the upward branching by the similar natural tendency of fire to
travel upwards. For he misinterprets up and down; up and down are not for all
things what they are for the whole Cosmos: if we are to distinguish and identify
organs according to their functions, the roots of plants are analogous to the
head in animals. Further, we must ask what is the force that holds together the
earth and the fire which tend to travel in contrary directions; if there is no
counteracting force, they will be torn asunder; if there is, this must be the
soul and the cause of nutrition and growth. By some the element of fire is held
to be the cause of nutrition and growth, for it alone of the primary bodies or
elements is observed to feed and increase itself. Hence the suggestion that in
both plants and animals it is it which is the operative force. A concurrent
cause in a sense it certainly is, but not the principal cause, that is rather
the soul; for while the growth of fire goes on without limit so long as there is
a supply of fuel, in the case of all complex wholes formed in the course of
nature there is a limit or ratio which determines their size and increase, and
limit and ratio are marks of soul but not of fire, and belong to the side of
formulable essence rather than that of matter.

Nutrition and reproduction are due to one and the same
psychic power. It is necessary first to give precision to our account of food,
for it is by this function of absorbing food that this psychic power is
distinguished from all the others. The current view is that what serves as food
to a living thing is what is contrary to it-not that in every pair of contraries
each is food to the other: to be food a contrary must not only be transformable
into the other and vice versa, it must also in so doing increase the bulk of the
other. Many a contrary is transformed into its other and vice versa, where
neither is even a quantum and so cannot increase in bulk, e.g. an invalid into a
healthy subject. It is clear that not even those contraries which satisfy both
the conditions mentioned above are food to one another in precisely the same
sense; water may be said to feed fire, but not fire water. Where the members of
the pair are elementary bodies only one of the contraries, it would appear, can
be said to feed the other. But there is a difficulty here. One set of thinkers
assert that like fed, as well as increased in amount, by like. Another set, as
we have said, maintain the very reverse, viz. that what feeds and what is fed
are contrary to one another; like, they argue, is incapable of being affected by
like; but food is changed in the process of digestion, and change is always to
what is opposite or to what is intermediate. Further, food is acted upon by what
is nourished by it, not the other way round, as timber is worked by a carpenter
and not conversely; there is a change in the carpenter but it is merely a change
from not-working to working. In answering this problem it makes all the
difference whether we mean by 'the food' the 'finished' or the 'raw' product. If
we use the word food of both, viz. of the completely undigested and the
completely digested matter, we can justify both the rival accounts of it; taking
food in the sense of undigested matter, it is the contrary of what is fed by it,
taking it as digested it is like what is fed by it. Consequently it is clear
that in a certain sense we may say that both parties are right, both wrong.

Since nothing except what is alive can be fed, what is fed
is the besouled body and just because it has soul in it. Hence food is
essentially related to what has soul in it. Food has a power which is other than
the power to increase the bulk of what is fed by it; so far forth as what has
soul in it is a quantum, food may increase its quantity, but it is only so far
as what has soul in it is a 'this-somewhat' or substance that food acts as food;
in that case it maintains the being of what is fed, and that continues to be
what it is so long as the process of nutrition continues. Further, it is the
agent in generation, i.e. not the generation of the individual fed but the
reproduction of another like it; the substance of the individual fed is already
in existence; the existence of no substance is a self-generation but only a
self-maintenance.

Hence the psychic power which we are now studying may be
described as that which tends to maintain whatever has this power in it of
continuing such as it was, and food helps it to do its work. That is why, if
deprived of food, it must cease to be.

The process of nutrition involves three factors, (a) what
is fed, (b) that wherewith it is fed, (c) what does the feeding; of these (c) is
the first soul, (a) the body which has that soul in it, (b) the food. But since
it is right to call things after the ends they realize, and the end of this soul
is to generate another being like that in which it is, the first soul ought to
be named the reproductive soul. The expression (b) 'wherewith it is fed' is
ambiguous just as is the expression 'wherewith the ship is steered'; that may
mean either (i) the hand or (ii) the rudder, i.e. either (i) what is moved and
sets in movement, or (ii) what is merely moved. We can apply this analogy here
if we recall that all food must be capable of being digested, and that what
produces digestion is warmth; that is why everything that has soul in it
possesses warmth.

We have now given an outline account of the nature of food;
further details must be given in the appropriate place.

5

Having made these distinctions let us now speak of
sensation in the widest sense. Sensation depends, as we have said, on a process
of movement or affection from without, for it is held to be some sort of change
of quality. Now some thinkers assert that like is affected only by like; in what
sense this is possible and in what sense impossible, we have explained in our
general discussion of acting and being acted upon.

Here arises a problem: why do we not perceive the senses
themselves as well as the external objects of sense, or why without the
stimulation of external objects do they not produce sensation, seeing that they
contain in themselves fire, earth, and all the other elements, which are the
direct or indirect objects is so of sense? It is clear that what is sensitive is
only potentially, not actually. The power of sense is parallel to what is
combustible, for that never ignites itself spontaneously, but requires an agent
which has the power of starting ignition; otherwise it could have set itself on
fire, and would not have needed actual fire to set it ablaze.

In reply we must recall that we use the word 'perceive' in
two ways, for we say (a) that what has the power to hear or see, 'sees' or
'hears', even though it is at the moment asleep, and also (b) that what is
actually seeing or hearing, 'sees' or 'hears'. Hence 'sense' too must have two
meanings, sense potential, and sense actual. Similarly 'to be a sentient' means
either (a) to have a certain power or (b) to manifest a certain activity. To
begin with, for a time, let us speak as if there were no difference between (i)
being moved or affected, and (ii) being active, for movement is a kind of
activity-an imperfect kind, as has elsewhere been explained. Everything that is
acted upon or moved is acted upon by an agent which is actually at work. Hence
it is that in one sense, as has already been stated, what acts and what is acted
upon are like, in another unlike, i.e. prior to and during the change the two
factors are unlike, after it like.

But we must now distinguish not only between what is
potential and what is actual but also different senses in which things can be
said to be potential or actual; up to now we have been speaking as if each of
these phrases had only one sense. We can speak of something as 'a knower' either
(a) as when we say that man is a knower, meaning that man falls within the class
of beings that know or have knowledge, or (b) as when we are speaking of a man
who possesses a knowledge of grammar; each of these is so called as having in
him a certain potentiality, but there is a difference between their respective
potentialities, the one (a) being a potential knower, because his kind or matter
is such and such, the other (b), because he can in the absence of any external
counteracting cause realize his knowledge in actual knowing at will. This
implies a third meaning of 'a knower' (c), one who is already realizing his
knowledge-he is a knower in actuality and in the most proper sense is knowing,
e.g. this A. Both the former are potential knowers, who realize their respective
potentialities, the one (a) by change of quality, i.e. repeated transitions from
one state to its opposite under instruction, the other (b) by the transition
from the inactive possession of sense or grammar to their active exercise. The
two kinds of transition are distinct.

Also the expression 'to be acted upon' has more than one
meaning; it may mean either (a) the extinction of one of two contraries by the
other, or (b) the maintenance of what is potential by the agency of what is
actual and already like what is acted upon, with such likeness as is compatible
with one's being actual and the other potential. For what possesses knowledge
becomes an actual knower by a transition which is either not an alteration of it
at all (being in reality a development into its true self or actuality) or at
least an alteration in a quite different sense from the usual meaning.

Hence it is wrong to speak of a wise man as being 'altered'
when he uses his wisdom, just as it would be absurd to speak of a builder as
being altered when he is using his skill in building a house.

What in the case of knowing or understanding leads from
potentiality to actuality ought not to be called teaching but something else.
That which starting with the power to know learns or acquires knowledge through
the agency of one who actually knows and has the power of teaching either (a)
ought not to be said 'to be acted upon' at all or (b) we must recognize two
senses of alteration, viz. (i) the substitution of one quality for another, the
first being the contrary of the second, or (ii) the development of an existent
quality from potentiality in the direction of fixity or nature.

In the case of what is to possess sense, the first
transition is due to the action of the male parent and takes place before birth
so that at birth the living thing is, in respect of sensation, at the stage
which corresponds to the possession of knowledge. Actual sensation corresponds
to the stage of the exercise of knowledge. But between the two cases compared
there is a difference; the objects that excite the sensory powers to activity,
the seen, the heard, &c., are outside. The ground of this difference is that
what actual sensation apprehends is individuals, while what knowledge apprehends
is universals, and these are in a sense within the soul. That is why a man can
exercise his knowledge when he wishes, but his sensation does not depend upon
himself a sensible object must be there. A similar statement must be made about
our knowledge of what is sensible-on the same ground, viz. that the sensible
objects are individual and external.

A later more appropriate occasion may be found thoroughly
to clear up all this. At present it must be enough to recognize the distinctions
already drawn; a thing may be said to be potential in either of two senses, (a)
in the sense in which we might say of a boy that he may become a general or (b)
in the sense in which we might say the same of an adult, and there are two
corresponding senses of the term 'a potential sentient'. There are no separate
names for the two stages of potentiality; we have pointed out that they are
different and how they are different. We cannot help using the incorrect terms
'being acted upon or altered' of the two transitions involved. As we have said,
has the power of sensation is potentially like what the perceived object is
actually; that is, while at the beginning of the process of its being acted upon
the two interacting factors are dissimilar, at the end the one acted upon is
assimilated to the other and is identical in quality with it.

6

In dealing with each of the senses we shall have first to
speak of the objects which are perceptible by each. The term 'object of sense'
covers three kinds of objects, two kinds of which are, in our language, directly
perceptible, while the remaining one is only incidentally perceptible. Of the
first two kinds one (a) consists of what is perceptible by a single sense, the
other (b) of what is perceptible by any and all of the senses. I call by the
name of special object of this or that sense that which cannot be perceived by
any other sense than that one and in respect of which no error is possible; in
this sense colour is the special object of sight, sound of hearing, flavour of
taste. Touch, indeed, discriminates more than one set of different qualities.
Each sense has one kind of object which it discerns, and never errs in reporting
that what is before it is colour or sound (though it may err as to what it is
that is coloured or where that is, or what it is that is sounding or where that
is.) Such objects are what we propose to call the special objects of this or
that sense.

'Common sensibles' are movement, rest, number, figure,
magnitude; these are not peculiar to any one sense, but are common to all. There
are at any rate certain kinds of movement which are perceptible both by touch
and by sight.

We speak of an incidental object of sense where e.g. the
white object which we see is the son of Diares; here because 'being the son of
Diares' is incidental to the directly visible white patch we speak of the son of
Diares as being (incidentally) perceived or seen by us. Because this is only
incidentally an object of sense, it in no way as such affects the senses. Of the
two former kinds, both of which are in their own nature perceptible by sense,
the first kind-that of special objects of the several senses-constitute the
objects of sense in the strictest sense of the term and it is to them that in
the nature of things the structure of each several sense is adapted.

7

The object of sight is the visible, and what is visible is
(a) colour and (b) a certain kind of object which can be described in words but
which has no single name; what we mean by (b) will be abundantly clear as we
proceed. Whatever is visible is colour and colour is what lies upon what is in
its own nature visible; 'in its own nature' here means not that visibility is
involved in the definition of what thus underlies colour, but that that
substratum contains in itself the cause of visibility. Every colour has in it
the power to set in movement what is actually transparent; that power
constitutes its very nature. That is why it is not visible except with the help
of light; it is only in light that the colour of a thing is seen. Hence our
first task is to explain what light is.

Now there clearly is something which is transparent, and by
'transparent' I mean what is visible, and yet not visible in itself, but rather
owing its visibility to the colour of something else; of this character are air,
water, and many solid bodies. Neither air nor water is transparent because it is
air or water; they are transparent because each of them has contained in it a
certain substance which is the same in both and is also found in the eternal
body which constitutes the uppermost shell of the physical Cosmos. Of this
substance light is the activity-the activity of what is transparent so far forth
as it has in it the determinate power of becoming transparent; where this power
is present, there is also the potentiality of the contrary, viz. darkness. Light
is as it were the proper colour of what is transparent, and exists whenever the
potentially transparent is excited to actuality by the influence of fire or
something resembling 'the uppermost body'; for fire too contains something which
is one and the same with the substance in question.

We have now explained what the transparent is and what
light is; light is neither fire nor any kind whatsoever of body nor an efflux
from any kind of body (if it were, it would again itself be a kind of body)-it
is the presence of fire or something resembling fire in what is transparent. It
is certainly not a body, for two bodies cannot be present in the same place. The
opposite of light is darkness; darkness is the absence from what is transparent
of the corresponding positive state above characterized; clearly therefore,
light is just the presence of that.

Empedocles (and with him all others who used the same forms
of expression) was wrong in speaking of light as 'travelling' or being at a
given moment between the earth and its envelope, its movement being unobservable
by us; that view is contrary both to the clear evidence of argument and to the
observed facts; if the distance traversed were short, the movement might have
been unobservable, but where the distance is from extreme East to extreme West,
the draught upon our powers of belief is too great.

What is capable of taking on colour is what in itself is
colourless, as what can take on sound is what is soundless; what is colourless
includes (a) what is transparent and (b) what is invisible or scarcely visible,
i.e. what is 'dark'. The latter (b) is the same as what is transparent, when it
is potentially, not of course when it is actually transparent; it is the same
substance which is now darkness, now light.

Not everything that is visible depends upon light for its
visibility. This is only true of the 'proper' colour of things. Some objects of
sight which in light are invisible, in darkness stimulate the sense; that is,
things that appear fiery or shining. This class of objects has no simple common
name, but instances of it are fungi, flesh, heads, scales, and eyes of fish. In
none of these is what is seen their own proper' colour. Why we see these at all
is another question. At present what is obvious is that what is seen in light is
always colour. That is why without the help of light colour remains invisible.
Its being colour at all means precisely its having in it the power to set in
movement what is already actually transparent, and, as we have seen, the
actuality of what is transparent is just light.

The following experiment makes the necessity of a medium
clear. If what has colour is placed in immediate contact with the eye, it cannot
be seen. Colour sets in movement not the sense organ but what is transparent,
e.g. the air, and that, extending continuously from the object to the organ,
sets the latter in movement. Democritus misrepresents the facts when he
expresses the opinion that if the interspace were empty one could distinctly see
an ant on the vault of the sky; that is an impossibility. Seeing is due to an
affection or change of what has the perceptive faculty, and it cannot be
affected by the seen colour itself; it remains that it must be affected by what
comes between. Hence it is indispensable that there be something in between-if
there were nothing, so far from seeing with greater distinctness, we should see
nothing at all.

We have now explained the cause why colour cannot be seen
otherwise than in light. Fire on the other hand is seen both in darkness and in
light; this double possibility follows necessarily from our theory, for it is
just fire that makes what is potentially transparent actually transparent.

The same account holds also of sound and smell; if the
object of either of these senses is in immediate contact with the organ no
sensation is produced. In both cases the object sets in movement only what lies
between, and this in turn sets the organ in movement: if what sounds or smells
is brought into immediate contact with the organ, no sensation will be produced.
The same, in spite of all appearances, applies also to touch and taste; why
there is this apparent difference will be clear later. What comes between in the
case of sounds is air; the corresponding medium in the case of smell has no
name. But, corresponding to what is transparent in the case of colour, there is
a quality found both in air and water, which serves as a medium for what has
smell-I say 'in water' because animals that live in water as well as those that
live on land seem to possess the sense of smell, and 'in air' because man and
all other land animals that breathe, perceive smells only when they breathe air
in. The explanation of this too will be given later.

8

Now let us, to begin with, make certain distinctions about
sound and hearing.

Sound may mean either of two things (a) actual, and (b)
potential, sound. There are certain things which, as we say, 'have no sound',
e.g. sponges or wool, others which have, e.g. bronze and in general all things
which are smooth and solid-the latter are said to have a sound because they can
make a sound, i.e. can generate actual sound between themselves and the organ of
hearing.

Actual sound requires for its occurrence (i, ii) two such
bodies and (iii) a space between them; for it is generated by an impact. Hence
it is impossible for one body only to generate a sound-there must be a body
impinging and a body impinged upon; what sounds does so by striking against
something else, and this is impossible without a movement from place to place.

As we have said, not all bodies can by impact on one
another produce sound; impact on wool makes no sound, while the impact on bronze
or any body which is smooth and hollow does. Bronze gives out a sound when
struck because it is smooth; bodies which are hollow owing to reflection repeat
the original impact over and over again, the body originally set in movement
being unable to escape from the concavity.

Further, we must remark that sound is heard both in air and
in water, though less distinctly in the latter. Yet neither air nor water is the
principal cause of sound. What is required for the production of sound is an
impact of two solids against one another and against the air. The latter
condition is satisfied when the air impinged upon does not retreat before the
blow, i.e. is not dissipated by it.

That is why it must be struck with a sudden sharp blow, if
it is to sound-the movement of the whip must outrun the dispersion of the air,
just as one might get in a stroke at a heap or whirl of sand as it was traveling
rapidly past.

An echo occurs, when, a mass of air having been unified,
bounded, and prevented from dissipation by the containing walls of a vessel, the
air originally struck by the impinging body and set in movement by it rebounds
from this mass of air like a ball from a wall. It is probable that in all
generation of sound echo takes place, though it is frequently only indistinctly
heard. What happens here must be analogous to what happens in the case of light;
light is always reflected-otherwise it would not be diffused and outside what
was directly illuminated by the sun there would be blank darkness; but this
reflected light is not always strong enough, as it is when it is reflected from
water, bronze, and other smooth bodies, to cast a shadow, which is the
distinguishing mark by which we recognize light.

It is rightly said that an empty space plays the chief part
in the production of hearing, for what people mean by 'the vacuum' is the air,
which is what causes hearing, when that air is set in movement as one continuous
mass; but owing to its friability it emits no sound, being dissipated by
impinging upon any surface which is not smooth. When the surface on which it
impinges is quite smooth, what is produced by the original impact is a united
mass, a result due to the smoothness of the surface with which the air is in
contact at the other end.

What has the power of producing sound is what has the power
of setting in movement a single mass of air which is continuous from the
impinging body up to the organ of hearing. The organ of hearing is physically
united with air, and because it is in air, the air inside is moved concurrently
with the air outside. Hence animals do not hear with all parts of their bodies,
nor do all parts admit of the entrance of air; for even the part which can be
moved and can sound has not air everywhere in it. Air in itself is, owing to its
friability, quite soundless; only when its dissipation is prevented is its
movement sound. The air in the ear is built into a chamber just to prevent this
dissipating movement, in order that the animal may accurately apprehend all
varieties of the movements of the air outside. That is why we hear also in
water, viz. because the water cannot get into the air chamber or even, owing to
the spirals, into the outer ear. If this does happen, hearing ceases, as it also
does if the tympanic membrane is damaged, just as sight ceases if the membrane
covering the pupil is damaged. It is also a test of deafness whether the ear
does or does not reverberate like a horn; the air inside the ear has always a
movement of its own, but the sound we hear is always the sounding of something
else, not of the organ itself. That is why we say that we hear with what is
empty and echoes, viz. because what we hear with is a chamber which contains a
bounded mass of air.

Which is it that 'sounds', the striking body or the struck?
Is not the answer 'it is both, but each in a different way'? Sound is a movement
of what can rebound from a smooth surface when struck against it. As we have
explained' not everything sounds when it strikes or is struck, e.g. if one
needle is struck against another, neither emits any sound. In order, therefore,
that sound may be generated, what is struck must be smooth, to enable the air to
rebound and be shaken off from it in one piece.

The distinctions between different sounding bodies show
themselves only in actual sound; as without the help of light colours remain
invisible, so without the help of actual sound the distinctions between acute
and grave sounds remain inaudible. Acute and grave are here metaphors,
transferred from their proper sphere, viz. that of touch, where they mean
respectively (a) what moves the sense much in a short time, (b) what moves the
sense little in a long time. Not that what is sharp really moves fast, and what
is grave, slowly, but that the difference in the qualities of the one and the
other movement is due to their respective speeds. There seems to be a sort of
parallelism between what is acute or grave to hearing and what is sharp or blunt
to touch; what is sharp as it were stabs, while what is blunt pushes, the one
producing its effect in a short, the other in a long time, so that the one is
quick, the other slow.

Let the foregoing suffice as an analysis of sound. Voice is
a kind of sound characteristic of what has soul in it; nothing that is without
soul utters voice, it being only by a metaphor that we speak of the voice of the
flute or the lyre or generally of what (being without soul) possesses the power
of producing a succession of notes which differ in length and pitch and timbre.
The metaphor is based on the fact that all these differences are found also in
voice. Many animals are voiceless, e.g. all non-sanuineous animals and among
sanguineous animals fish. This is just what we should expect, since voice is a
certain movement of air. The fish, like those in the Achelous, which are said to
have voice, really make the sounds with their gills or some similar organ. Voice
is the sound made by an animal, and that with a special organ. As we saw,
everything that makes a sound does so by the impact of something (a) against
something else, (b) across a space, (c) filled with air; hence it is only to be
expected that no animals utter voice except those which take in air. Once air is
inbreathed, Nature uses it for two different purposes, as the tongue is used
both for tasting and for articulating; in that case of the two functions tasting
is necessary for the animal's existence (hence it is found more widely
distributed), while articulate speech is a luxury subserving its possessor's
well-being; similarly in the former case Nature employs the breath both as an
indispensable means to the regulation of the inner temperature of the living
body and also as the matter of articulate voice, in the interests of its
possessor's well-being. Why its former use is indispensable must be discussed
elsewhere.

The organ of respiration is the windpipe, and the organ to
which this is related as means to end is the lungs. The latter is the part of
the body by which the temperature of land animals is raised above that of all
others. But what primarily requires the air drawn in by respiration is not only
this but the region surrounding the heart. That is why when animals breathe the
air must penetrate inwards.

Voice then is the impact of the inbreathed air against the
'windpipe', and the agent that produces the impact is the soul resident in these
parts of the body. Not every sound, as we said, made by an animal is voice (even
with the tongue we may merely make a sound which is not voice, or without the
tongue as in coughing); what produces the impact must have soul in it and must
be accompanied by an act of imagination, for voice is a sound with a meaning,
and is not merely the result of any impact of the breath as in coughing; in
voice the breath in the windpipe is used as an instrument to knock with against
the walls of the windpipe. This is confirmed by our inability to speak when we
are breathing either out or in-we can only do so by holding our breath; we make
the movements with the breath so checked. It is clear also why fish are
voiceless; they have no windpipe. And they have no windpipe because they do not
breathe or take in air. Why they do not is a question belonging to another
inquiry.

9

Smell and its object are much less easy to determine than
what we have hitherto discussed; the distinguishing characteristic of the object
of smell is less obvious than those of sound or colour. The ground of this is
that our power of smell is less discriminating and in general inferior to that
of many species of animals; men have a poor sense of smell and our apprehension
of its proper objects is inseparably bound up with and so confused by pleasure
and pain, which shows that in us the organ is inaccurate. It is probable that
there is a parallel failure in the perception of colour by animals that have
hard eyes: probably they discriminate differences of colour only by the presence
or absence of what excites fear, and that it is thus that human beings
distinguish smells. It seems that there is an analogy between smell and taste,
and that the species of tastes run parallel to those of smells-the only
difference being that our sense of taste is more discriminating than our sense
of smell, because the former is a modification of touch, which reaches in man
the maximum of discriminative accuracy. While in respect of all the other senses
we fall below many species of animals, in respect of touch we far excel all
other species in exactness of discrimination. That is why man is the most
intelligent of all animals. This is confirmed by the fact that it is to
differences in the organ of touch and to nothing else that the differences
between man and man in respect of natural endowment are due; men whose flesh is
hard are ill-endowed by nature, men whose flesh is soft, wellendowed.

As flavours may be divided into (a) sweet, (b) bitter, so
with smells. In some things the flavour and the smell have the same quality,
i.e. both are sweet or both bitter, in others they diverge. Similarly a smell,
like a flavour, may be pungent, astringent, acid, or succulent. But, as we said,
because smells are much less easy to discriminate than flavours, the names of
these varieties are applied to smells only metaphorically; for example 'sweet'
is extended from the taste to the smell of saffron or honey, 'pungent' to that
of thyme, and so on.

In the same sense in which hearing has for its object both
the audible and the inaudible, sight both the visible and the invisible, smell
has for its object both the odorous and the inodorous. 'Inodorous' may be either
(a) what has no smell at all, or (b) what has a small or feeble smell. The same
ambiguity lurks in the word 'tasteless'.

Smelling, like the operation of the senses previously
examined, takes place through a medium, i.e. through air or water-I add water,
because water-animals too (both sanguineous and non-sanguineous) seem to smell
just as much as land-animals; at any rate some of them make directly for their
food from a distance if it has any scent. That is why the following facts
constitute a problem for us. All animals smell in the same way, but man smells
only when he inhales; if he exhales or holds his breath, he ceases to smell, no
difference being made whether the odorous object is distant or near, or even
placed inside the nose and actually on the wall of the nostril; it is a
disability common to all the senses not to perceive what is in immediate contact
with the organ of sense, but our failure to apprehend what is odorous without
the help of inhalation is peculiar (the fact is obvious on making the
experiment). Now since bloodless animals do not breathe, they must, it might be
argued, have some novel sense not reckoned among the usual five. Our reply must
be that this is impossible, since it is scent that is perceived; a sense that
apprehends what is odorous and what has a good or bad odour cannot be anything
but smell. Further, they are observed to be deleteriously effected by the same
strong odours as man is, e.g. bitumen, sulphur, and the like. These animals must
be able to smell without being able to breathe. The probable explanation is that
in man the organ of smell has a certain superiority over that in all other
animals just as his eyes have over those of hard-eyed animals. Man's eyes have
in the eyelids a kind of shelter or envelope, which must be shifted or drawn
back in order that we may see, while hardeyed animals have nothing of the kind,
but at once see whatever presents itself in the transparent medium. Similarly in
certain species of animals the organ of smell is like the eye of hard-eyed
animals, uncurtained, while in others which take in air it probably has a
curtain over it, which is drawn back in inhalation, owing to the dilating of the
veins or pores. That explains also why such animals cannot smell under water; to
smell they must first inhale, and that they cannot do under water.

Smells come from what is dry as flavours from what is
moist. Consequently the organ of smell is potentially dry.

10

What can be tasted is always something that can be touched,
and just for that reason it cannot be perceived through an interposed foreign
body, for touch means the absence of any intervening body. Further, the
flavoured and tasteable body is suspended in a liquid matter, and this is
tangible. Hence, if we lived in water, we should perceive a sweet object
introduced into the water, but the water would not be the medium through which
we perceived; our perception would be due to the solution of the sweet substance
in what we imbibed, just as if it were mixed with some drink. There is no
parallel here to the perception of colour, which is due neither to any blending
of anything with anything, nor to any efflux of anything from anything. In the
case of taste, there is nothing corresponding to the medium in the case of the
senses previously discussed; but as the object of sight is colour, so the object
of taste is flavour. But nothing excites a perception of flavour without the
help of liquid; what acts upon the sense of taste must be either actually or
potentially liquid like what is saline; it must be both (a) itself easily
dissolved, and (b) capable of dissolving along with itself the tongue. Taste
apprehends both (a) what has taste and (b) what has no taste, if we mean by (b)
what has only a slight or feeble flavour or what tends to destroy the sense of
taste. In this it is exactly parallel to sight, which apprehends both what is
visible and what is invisible (for darkness is invisible and yet is
discriminated by sight; so is, in a different way, what is over brilliant), and
to hearing, which apprehends both sound and silence, of which the one is audible
and the other inaudible, and also over-loud sound. This corresponds in the case
of hearing to over-bright light in the case of sight. As a faint sound is
'inaudible', so in a sense is a loud or violent sound. The word 'invisible' and
similar privative terms cover not only (a) what is simply without some power,
but also (b) what is adapted by nature to have it but has not it or has it only
in a very low degree, as when we say that a species of swallow is 'footless' or
that a variety of fruit is 'stoneless'. So too taste has as its object both what
can be tasted and the tasteless-the latter in the sense of what has little
flavour or a bad flavour or one destructive of taste. The difference between
what is tasteless and what is not seems to rest ultimately on that between what
is drinkable and what is undrinkable both are tasteable, but the latter is bad
and tends to destroy taste, while the former is the normal stimulus of taste.
What is drinkable is the common object of both touch and taste.

Since what can be tasted is liquid, the organ for its
perception cannot be either (a) actually liquid or (b) incapable of becoming
liquid. Tasting means a being affected by what can be tasted as such; hence the
organ of taste must be liquefied, and so to start with must be non-liquid but
capable of liquefaction without loss of its distinctive nature. This is
confirmed by the fact that the tongue cannot taste either when it is too dry or
when it is too moist; in the latter case what occurs is due to a contact with
the pre-existent moisture in the tongue itself, when after a foretaste of some
strong flavour we try to taste another flavour; it is in this way that sick
persons find everything they taste bitter, viz. because, when they taste, their
tongues are overflowing with bitter moisture.

The species of flavour are, as in the case of colour, (a)
simple, i.e. the two contraries, the sweet and the bitter, (b) secondary, viz.
(i) on the side of the sweet, the succulent, (ii) on the side of the bitter, the
saline, (iii) between these come the pungent, the harsh, the astringent, and the
acid; these pretty well exhaust the varieties of flavour. It follows that what
has the power of tasting is what is potentially of that kind, and that what is
tasteable is what has the power of making it actually what it itself already is.

11

Whatever can be said of what is tangible, can be said of
touch, and vice versa; if touch is not a single sense but a group of senses,
there must be several kinds of what is tangible. It is a problem whether touch
is a single sense or a group of senses. It is also a problem, what is the organ
of touch; is it or is it not the flesh (including what in certain animals is
homologous with flesh)? On the second view, flesh is 'the medium' of touch, the
real organ being situated farther inward. The problem arises because the field
of each sense is according to the accepted view determined as the range between
a single pair of contraries, white and black for sight, acute and grave for
hearing, bitter and sweet for taste; but in the field of what is tangible we
find several such pairs, hot cold, dry moist, hard soft, &c. This problem
finds a partial solution, when it is recalled that in the case of the other
senses more than one pair of contraries are to be met with, e.g. in sound not
only acute and grave but loud and soft, smooth and rough, &c.; there are
similar contrasts in the field of colour. Nevertheless we are unable clearly to
detect in the case of touch what the single subject is which underlies the
contrasted qualities and corresponds to sound in the case of hearing.

To the question whether the organ of touch lies inward or
not (i.e. whether we need look any farther than the flesh), no indication in
favour of the second answer can be drawn from the fact that if the object comes
into contact with the flesh it is at once perceived. For even under present
conditions if the experiment is made of making a web and stretching it tight
over the flesh, as soon as this web is touched the sensation is reported in the
same manner as before, yet it is clear that the or is gan is not in this
membrane. If the membrane could be grown on to the flesh, the report would
travel still quicker. The flesh plays in touch very much the same part as would
be played in the other senses by an air-envelope growing round our body; had we
such an envelope attached to us we should have supposed that it was by a single
organ that we perceived sounds, colours, and smells, and we should have taken
sight, hearing, and smell to be a single sense. But as it is, because that
through which the different movements are transmitted is not naturally attached
to our bodies, the difference of the various sense-organs is too plain to miss.
But in the case of touch the obscurity remains.

There must be such a naturally attached 'medium' as flesh,
for no living body could be constructed of air or water; it must be something
solid. Consequently it must be composed of earth along with these, which is just
what flesh and its analogue in animals which have no true flesh tend to be.
Hence of necessity the medium through which are transmitted the manifoldly
contrasted tactual qualities must be a body naturally attached to the organism.
That they are manifold is clear when we consider touching with the tongue; we
apprehend at the tongue all tangible qualities as well as flavour. Suppose all
the rest of our flesh was, like the tongue, sensitive to flavour, we should have
identified the sense of taste and the sense of touch; what saves us from this
identification is the fact that touch and taste are not always found together in
the same part of the body. The following problem might be raised. Let us assume
that every body has depth, i.e. has three dimensions, and that if two bodies
have a third body between them they cannot be in contact with one another; let
us remember that what is liquid is a body and must be or contain water, and that
if two bodies touch one another under water, their touching surfaces cannot be
dry, but must have water between, viz. the water which wets their bounding
surfaces; from all this it follows that in water two bodies cannot be in contact
with one another. The same holds of two bodies in air-air being to bodies in air
precisely what water is to bodies in water-but the facts are not so evident to
our observation, because we live in air, just as animals that live in water
would not notice that the things which touch one another in water have wet
surfaces. The problem, then, is: does the perception of all objects of sense
take place in the same way, or does it not, e.g. taste and touch requiring
contact (as they are commonly thought to do), while all other senses perceive
over a distance? The distinction is unsound; we perceive what is hard or soft,
as well as the objects of hearing, sight, and smell, through a 'medium', only
that the latter are perceived over a greater distance than the former; that is
why the facts escape our notice. For we do perceive everything through a medium;
but in these cases the fact escapes us. Yet, to repeat what we said before, if
the medium for touch were a membrane separating us from the object without our
observing its existence, we should be relatively to it in the same condition as
we are now to air or water in which we are immersed; in their case we fancy we
can touch objects, nothing coming in between us and them. But there remains this
difference between what can be touched and what can be seen or can sound; in the
latter two cases we perceive because the medium produces a certain effect upon
us, whereas in the perception of objects of touch we are affected not by but
along with the medium; it is as if a man were struck through his shield, where
the shock is not first given to the shield and passed on to the man, but the
concussion of both is simultaneous.

In general, flesh and the tongue are related to the real
organs of touch and taste, as air and water are to those of sight, hearing, and
smell. Hence in neither the one case nor the other can there be any perception
of an object if it is placed immediately upon the organ, e.g. if a white object
is placed on the surface of the eye. This again shows that what has the power of
perceiving the tangible is seated inside. Only so would there be a complete
analogy with all the other senses. In their case if you place the object on the
organ it is not perceived, here if you place it on the flesh it is perceived;
therefore flesh is not the organ but the medium of touch.

What can be touched are distinctive qualities of body as
body; by such differences I mean those which characterize the elements, viz, hot
cold, dry moist, of which we have spoken earlier in our treatise on the
elements. The organ for the perception of these is that of touch-that part of
the body in which primarily the sense of touch resides. This is that part which
is potentially such as its object is actually: for all sense-perception is a
process of being so affected; so that that which makes something such as it
itself actually is makes the other such because the other is already potentially
such. That is why when an object of touch is equally hot and cold or hard and
soft we cannot perceive; what we perceive must have a degree of the sensible
quality lying beyond the neutral point. This implies that the sense itself is a
'mean' between any two opposite qualities which determine the field of that
sense. It is to this that it owes its power of discerning the objects in that
field. What is 'in the middle' is fitted to discern; relatively to either
extreme it can put itself in the place of the other. As what is to perceive both
white and black must, to begin with, be actually neither but potentially either
(and so with all the other sense-organs), so the organ of touch must be neither
hot nor cold.

Further, as in a sense sight had for its object both what
was visible and what was invisible (and there was a parallel truth about all the
other senses discussed), so touch has for its object both what is tangible and
what is intangible. Here by 'intangible' is meant (a) what like air possesses
some quality of tangible things in a very slight degree and (b) what possesses
it in an excessive degree, as destructive things do.

We have now given an outline account of each of the several
senses.

12

The following results applying to any and every sense may
now be formulated.

(A) By a 'sense' is meant what has the power of receiving
into itself the sensible forms of things without the matter. This must be
conceived of as taking place in the way in which a piece of wax takes on the
impress of a signet-ring without the iron or gold; we say that what produces the
impression is a signet of bronze or gold, but its particular metallic
constitution makes no difference: in a similar way the sense is affected by what
is coloured or flavoured or sounding, but it is indifferent what in each case
the substance is; what alone matters is what quality it has, i.e. in what ratio
its constituents are combined.

(B) By 'an organ of sense' is meant that in which
ultimately such a power is seated.

The sense and its organ are the same in fact, but their
essence is not the same. What perceives is, of course, a spatial magnitude, but
we must not admit that either the having the power to perceive or the sense
itself is a magnitude; what they are is a certain ratio or power in a magnitude.
This enables us to explain why objects of sense which possess one of two
opposite sensible qualities in a degree largely in excess of the other opposite
destroy the organs of sense; if the movement set up by an object is too strong
for the organ, the equipoise of contrary qualities in the organ, which just is
its sensory power, is disturbed; it is precisely as concord and tone are
destroyed by too violently twanging the strings of a lyre. This explains also
why plants cannot perceive. in spite of their having a portion of soul in them
and obviously being affected by tangible objects themselves; for undoubtedly
their temperature can be lowered or raised. The explanation is that they have no
mean of contrary qualities, and so no principle in them capable of taking on the
forms of sensible objects without their matter; in the case of plants the
affection is an affection by form-and-matter together. The problem might be
raised: Can what cannot smell be said to be affected by smells or what cannot
see by colours, and so on? It might be said that a smell is just what can be
smelt, and if it produces any effect it can only be so as to make something
smell it, and it might be argued that what cannot smell cannot be affected by
smells and further that what can smell can be affected by it only in so far as
it has in it the power to smell (similarly with the proper objects of all the
other senses). Indeed that this is so is made quite evident as follows. Light or
darkness, sounds and smells leave bodies quite unaffected; what does affect
bodies is not these but the bodies which are their vehicles, e.g. what splits
the trunk of a tree is not the sound of the thunder but the air which
accompanies thunder. Yes, but, it may be objected, bodies are affected by what
is tangible and by flavours. If not, by what are things that are without soul
affected, i.e. altered in quality? Must we not, then, admit that the objects of
the other senses also may affect them? Is not the true account this, that all
bodies are capable of being affected by smells and sounds, but that some on
being acted upon, having no boundaries of their own, disintegrate, as in the
instance of air, which does become odorous, showing that some effect is produced
on it by what is odorous? But smelling is more than such an affection by what is
odorous-what more? Is not the answer that, while the air owing to the momentary
duration of the action upon it of what is odorous does itself become perceptible
to the sense of smell, smelling is an observing of the result produced?

Book III

1

THAT there is no sixth sense in addition to the five
enumerated-sight, hearing, smell, taste, touch-may be established by the
following considerations:

If we have actually sensation of everything of which touch
can give us sensation (for all the qualities of the tangible qua tangible are
perceived by us through touch); and if absence of a sense necessarily involves
absence of a sense-organ; and if (1) all objects that we perceive by immediate
contact with them are perceptible by touch, which sense we actually possess, and
(2) all objects that we perceive through media, i.e. without immediate contact,
are perceptible by or through the simple elements, e.g. air and water (and this
is so arranged that (a) if more than one kind of sensible object is perceivable
through a single medium, the possessor of a sense-organ homogeneous with that
medium has the power of perceiving both kinds of objects; for example, if the
sense-organ is made of air, and air is a medium both for sound and for colour;
and that (b) if more than one medium can transmit the same kind of sensible
objects, as e.g. water as well as air can transmit colour, both being
transparent, then the possessor of either alone will be able to perceive the
kind of objects transmissible through both); and if of the simple elements two
only, air and water, go to form sense-organs (for the pupil is made of water,
the organ of hearing is made of air, and the organ of smell of one or other of
these two, while fire is found either in none or in all-warmth being an
essential condition of all sensibility-and earth either in none or, if anywhere,
specially mingled with the components of the organ of touch; wherefore it would
remain that there can be no sense-organ formed of anything except water and
air); and if these sense-organs are actually found in certain animals;-then all
the possible senses are possessed by those animals that are not imperfect or
mutilated (for even the mole is observed to have eyes beneath its skin); so
that, if there is no fifth element and no property other than those which belong
to the four elements of our world, no sense can be wanting to such animals.

Further, there cannot be a special sense-organ for the
common sensibles either, i.e. the objects which we perceive incidentally through
this or that special sense, e.g. movement, rest, figure, magnitude, number,
unity; for all these we perceive by movement, e.g. magnitude by movement, and
therefore also figure (for figure is a species of magnitude), what is at rest by
the absence of movement: number is perceived by the negation of continuity, and
by the special sensibles; for each sense perceives one class of sensible
objects. So that it is clearly impossible that there should be a special sense
for any one of the common sensibles, e.g. movement; for, if that were so, our
perception of it would be exactly parallel to our present perception of what is
sweet by vision. That is so because we have a sense for each of the two
qualities, in virtue of which when they happen to meet in one sensible object we
are aware of both contemporaneously. If it were not like this our perception of
the common qualities would always be incidental, i.e. as is the perception of
Cleon's son, where we perceive him not as Cleon's son but as white, and the
white thing which we really perceive happens to be Cleon's son.

But in the case of the common sensibles there is already in
us a general sensibility which enables us to perceive them directly; there is
therefore no special sense required for their perception: if there were, our
perception of them would have been exactly like what has been above described.

The senses perceive each other's special objects
incidentally; not because the percipient sense is this or that special sense,
but because all form a unity: this incidental perception takes place whenever
sense is directed at one and the same moment to two disparate qualities in one
and the same object, e.g. to the bitterness and the yellowness of bile, the
assertion of the identity of both cannot be the act of either of the senses;
hence the illusion of sense, e.g. the belief that if a thing is yellow it is
bile.

It might be asked why we have more senses than one. Is it
to prevent a failure to apprehend the common sensibles, e.g. movement,
magnitude, and number, which go along with the special sensibles? Had we no
sense but sight, and that sense no object but white, they would have tended to
escape our notice and everything would have merged for us into an
indistinguishable identity because of the concomitance of colour and magnitude.
As it is, the fact that the common sensibles are given in the objects of more
than one sense reveals their distinction from each and all of the special
sensibles.

2

Since it is through sense that we are aware that we are
seeing or hearing, it must be either by sight that we are aware of seeing, or by
some sense other than sight. But the sense that gives us this new sensation must
perceive both sight and its object, viz. colour: so that either (1) there will
be two senses both percipient of the same sensible object, or (2) the sense must
be percipient of itself. Further, even if the sense which perceives sight were
different from sight, we must either fall into an infinite regress, or we must
somewhere assume a sense which is aware of itself. If so, we ought to do this in
the first case.

This presents a difficulty: if to perceive by sight is just
to see, and what is seen is colour (or the coloured), then if we are to see that
which sees, that which sees originally must be coloured. It is clear therefore
that 'to perceive by sight' has more than one meaning; for even when we are not
seeing, it is by sight that we discriminate darkness from light, though not in
the same way as we distinguish one colour from another. Further, in a sense even
that which sees is coloured; for in each case the sense-organ is capable of
receiving the sensible object without its matter. That is why even when the
sensible objects are gone the sensings and imaginings continue to exist in the
sense-organs.

The activity of the sensible object and that of the
percipient sense is one and the same activity, and yet the distinction between
their being remains. Take as illustration actual sound and actual hearing: a man
may have hearing and yet not be hearing, and that which has a sound is not
always sounding. But when that which can hear is actively hearing and which can
sound is sounding, then the actual hearing and the actual sound are merged in
one (these one might call respectively hearkening and sounding).

If it is true that the movement, both the acting and the
being acted upon, is to be found in that which is acted upon, both the sound and
the hearing so far as it is actual must be found in that which has the faculty
of hearing; for it is in the passive factor that the actuality of the active or
motive factor is realized; that is why that which causes movement may be at
rest. Now the actuality of that which can sound is just sound or sounding, and
the actuality of that which can hear is hearing or hearkening; 'sound' and
'hearing' are both ambiguous. The same account applies to the other senses and
their objects. For as the-acting-and-being-acted-upon is to be found in the
passive, not in the active factor, so also the actuality of the sensible object
and that of the sensitive subject are both realized in the latter. But while in
some cases each aspect of the total actuality has a distinct name, e.g. sounding
and hearkening, in some one or other is nameless, e.g. the actuality of sight is
called seeing, but the actuality of colour has no name: the actuality of the
faculty of taste is called tasting, but the actuality of flavour has no name.
Since the actualities of the sensible object and of the sensitive faculty are
one actuality in spite of the difference between their modes of being, actual
hearing and actual sounding appear and disappear from existence at one and the
same moment, and so actual savour and actual tasting, &c., while as
potentialities one of them may exist without the other. The earlier students of
nature were mistaken in their view that without sight there was no white or
black, without taste no savour. This statement of theirs is partly true, partly
false: 'sense' and 'the sensible object' are ambiguous terms, i.e. may denote
either potentialities or actualities: the statement is true of the latter, false
of the former. This ambiguity they wholly failed to notice.

If voice always implies a concord, and if the voice and the
hearing of it are in one sense one and the same, and if concord always implies a
ratio, hearing as well as what is heard must be a ratio. That is why the excess
of either the sharp or the flat destroys the hearing. (So also in the case of
savours excess destroys the sense of taste, and in the case of colours excessive
brightness or darkness destroys the sight, and in the case of smell excess of
strength whether in the direction of sweetness or bitterness is destructive.)
This shows that the sense is a ratio.

That is also why the objects of sense are (1) pleasant when
the sensible extremes such as acid or sweet or salt being pure and unmixed are
brought into the proper ratio; then they are pleasant: and in general what is
blended is more pleasant than the sharp or the flat alone; or, to touch, that
which is capable of being either warmed or chilled: the sense and the ratio are
identical: while (2) in excess the sensible extremes are painful or destructive.

Each sense then is relative to its particular group of
sensible qualities: it is found in a sense-organ as such and discriminates the
differences which exist within that group; e.g. sight discriminates white and
black, taste sweet and bitter, and so in all cases. Since we also discriminate
white from sweet, and indeed each sensible quality from every other, with what
do we perceive that they are different? It must be by sense; for what is before
us is sensible objects. (Hence it is also obvious that the flesh cannot be the
ultimate sense-organ: if it were, the discriminating power could not do its work
without immediate contact with the object.)

Therefore (1) discrimination between white and sweet cannot
be effected by two agencies which remain separate; both the qualities
discriminated must be present to something that is one and single. On any other
supposition even if I perceived sweet and you perceived white, the difference
between them would be apparent. What says that two things are different must be
one; for sweet is different from white. Therefore what asserts this difference
must be self-identical, and as what asserts, so also what thinks or perceives.
That it is not possible by means of two agencies which remain separate to
discriminate two objects which are separate, is therefore obvious; and that (it
is not possible to do this in separate movements of time may be seen' if we look
at it as follows. For as what asserts the difference between the good and the
bad is one and the same, so also the time at which it asserts the one to be
different and the other to be different is not accidental to the assertion (as
it is for instance when I now assert a difference but do not assert that there
is now a difference); it asserts thus-both now and that the objects are
different now; the objects therefore must be present at one and the same moment.
Both the discriminating power and the time of its exercise must be one and
undivided.

But, it may be objected, it is impossible that what is
self-identical should be moved at me and the same time with contrary movements
in so far as it is undivided, and in an undivided moment of time. For if what is
sweet be the quality perceived, it moves the sense or thought in this
determinate way, while what is bitter moves it in a contrary way, and what is
white in a different way. Is it the case then that what discriminates, though
both numerically one and indivisible, is at the same time divided in its being?
In one sense, it is what is divided that perceives two separate objects at once,
but in another sense it does so qua undivided; for it is divisible in its being
but spatially and numerically undivided. is not this impossible? For while it is
true that what is self-identical and undivided may be both contraries at once
potentially, it cannot be self-identical in its being-it must lose its unity by
being put into activity. It is not possible to be at once white and black, and
therefore it must also be impossible for a thing to be affected at one and the
same moment by the forms of both, assuming it to be the case that sensation and
thinking are properly so described.

The answer is that just as what is called a 'point' is, as
being at once one and two, properly said to be divisible, so here, that which
discriminates is qua undivided one, and active in a single moment of time, while
so far forth as it is divisible it twice over uses the same dot at one and the
same time. So far forth then as it takes the limit as two' it discriminates two
separate objects with what in a sense is divided: while so far as it takes it as
one, it does so with what is one and occupies in its activity a single moment of
time.

About the principle in virtue of which we say that animals
are percipient, let this discussion suffice.

3

There are two distinctive peculiarities by reference to
which we characterize the soul (1) local movement and (2) thinking,
discriminating, and perceiving. Thinking both speculative and practical is
regarded as akin to a form of perceiving; for in the one as well as the other
the soul discriminates and is cognizant of something which is. Indeed the
ancients go so far as to identify thinking and perceiving; e.g. Empedocles says
'For 'tis in respect of what is present that man's wit is increased', and again
'Whence it befalls them from time to time to think diverse thoughts', and
Homer's phrase 'For suchlike is man's mind' means the same. They all look upon
thinking as a bodily process like perceiving, and hold that like is known as
well as perceived by like, as I explained at the beginning of our discussion.
Yet they ought at the same time to have accounted for error also; for it is more
intimately connected with animal existence and the soul continues longer in the
state of error than in that of truth. They cannot escape the dilemma: either (1)
whatever seems is true (and there are some who accept this) or (2) error is
contact with the unlike; for that is the opposite of the knowing of like by
like.

But it is a received principle that error as well as
knowledge in respect to contraries is one and the same.

That perceiving and practical thinking are not identical is
therefore obvious; for the former is universal in the animal world, the latter
is found in only a small division of it. Further, speculative thinking is also
distinct from perceiving-I mean that in which we find rightness and
wrongness-rightness in prudence, knowledge, true opinion, wrongness in their
opposites; for perception of the special objects of sense is always free from
error, and is found in all animals, while it is possible to think falsely as
well as truly, and thought is found only where there is discourse of reason as
well as sensibility. For imagination is different from either perceiving or
discursive thinking, though it is not found without sensation, or judgement
without it. That this activity is not the same kind of thinking as judgement is
obvious. For imagining lies within our own power whenever we wish (e.g. we can
call up a picture, as in the practice of mnemonics by the use of mental images),
but in forming opinions we are not free: we cannot escape the alternative of
falsehood or truth. Further, when we think something to be fearful or
threatening, emotion is immediately produced, and so too with what is
encouraging; but when we merely imagine we remain as unaffected as persons who
are looking at a painting of some dreadful or encouraging scene. Again within
the field of judgement itself we find varieties, knowledge, opinion, prudence,
and their opposites; of the differences between these I must speak elsewhere.

Thinking is different from perceiving and is held to be in
part imagination, in part judgement: we must therefore first mark off the sphere
of imagination and then speak of judgement. If then imagination is that in
virtue of which an image arises for us, excluding metaphorical uses of the term,
is it a single faculty or disposition relative to images, in virtue of which we
discriminate and are either in error or not? The faculties in virtue of which we
do this are sense, opinion, science, intelligence.

That imagination is not sense is clear from the following
considerations: Sense is either a faculty or an activity, e.g. sight or seeing:
imagination takes place in the absence of both, as e.g. in dreams. (Again, sense
is always present, imagination not. If actual imagination and actual sensation
were the same, imagination would be found in all the brutes: this is held not to
be the case; e.g. it is not found in ants or bees or grubs. (Again, sensations
are always true, imaginations are for the most part false. (Once more, even in
ordinary speech, we do not, when sense functions precisely with regard to its
object, say that we imagine it to be a man, but rather when there is some
failure of accuracy in its exercise. And as we were saying before, visions
appear to us even when our eyes are shut. Neither is imagination any of the
things that are never in error: e.g. knowledge or intelligence; for imagination
may be false.

It remains therefore to see if it is opinion, for opinion
may be either true or false.

But opinion involves belief (for without belief in what we
opine we cannot have an opinion), and in the brutes though we often find
imagination we never find belief. Further, every opinion is accompanied by
belief, belief by conviction, and conviction by discourse of reason: while there
are some of the brutes in which we find imagination, without discourse of
reason. It is clear then that imagination cannot, again, be (1) opinion plus
sensation, or (2) opinion mediated by sensation, or (3) a blend of opinion and
sensation; this is impossible both for these reasons and because the content of
the supposed opinion cannot be different from that of the sensation (I mean that
imagination must be the blending of the perception of white with the opinion
that it is white: it could scarcely be a blend of the opinion that it is good
with the perception that it is white): to imagine is therefore (on this view)
identical with the thinking of exactly the same as what one in the strictest
sense perceives. But what we imagine is sometimes false though our
contemporaneous judgement about it is true; e.g. we imagine the sun to be a foot
in diameter though we are convinced that it is larger than the inhabited part of
the earth, and the following dilemma presents itself. Either (a while the fact
has not changed and the (observer has neither forgotten nor lost belief in the
true opinion which he had, that opinion has disappeared, or (b) if he retains it
then his opinion is at once true and false. A true opinion, however, becomes
false only when the fact alters without being noticed.

Imagination is therefore neither any one of the states
enumerated, nor compounded out of them.

But since when one thing has been set in motion another
thing may be moved by it, and imagination is held to be a movement and to be
impossible without sensation, i.e. to occur in beings that are percipient and to
have for its content what can be perceived, and since movement may be produced
by actual sensation and that movement is necessarily similar in character to the
sensation itself, this movement must be (1) necessarily (a) incapable of
existing apart from sensation, (b) incapable of existing except when we
perceive, (such that in virtue of its possession that in which it is found may
present various phenomena both active and passive, and (such that it may be
either true or false.

The reason of the last characteristic is as follows.
Perception (1) of the special objects of sense is never in error or admits the
least possible amount of falsehood. (2) That of the concomitance of the objects
concomitant with the sensible qualities comes next: in this case certainly we
may be deceived; for while the perception that there is white before us cannot
be false, the perception that what is white is this or that may be false. (3)
Third comes the perception of the universal attributes which accompany the
concomitant objects to which the special sensibles attach (I mean e.g. of
movement and magnitude); it is in respect of these that the greatest amount of
sense-illusion is possible.

The motion which is due to the activity of sense in these
three modes of its exercise will differ from the activity of sense; (1) the
first kind of derived motion is free from error while the sensation is present;
(2) and (3) the others may be erroneous whether it is present or absent,
especially when the object of perception is far off. If then imagination
presents no other features than those enumerated and is what we have described,
then imagination must be a movement resulting from an actual exercise of a power
of sense.

As sight is the most highly developed sense, the name
Phantasia (imagination) has been formed from Phaos (light) because it is not
possible to see without light.

And because imaginations remain in the organs of sense and
resemble sensations, animals in their actions are largely guided by them, some
(i.e. the brutes) because of the non-existence in them of mind, others (i.e.
men) because of the temporary eclipse in them of mind by feeling or disease or
sleep.

About imagination, what it is and why it exists, let so
much suffice.

4

Turning now to the part of the soul with which the soul
knows and thinks (whether this is separable from the others in definition only,
or spatially as well) we have to inquire (1) what differentiates this part, and
(2) how thinking can take place.

If thinking is like perceiving, it must be either a process
in which the soul is acted upon by what is capable of being thought, or a
process different from but analogous to that. The thinking part of the soul must
therefore be, while impassible, capable of receiving the form of an object; that
is, must be potentially identical in character with its object without being the
object. Mind must be related to what is thinkable, as sense is to what is
sensible.

Therefore, since everything is a possible object of
thought, mind in order, as Anaxagoras says, to dominate, that is, to know, must
be pure from all admixture; for the co-presence of what is alien to its nature
is a hindrance and a block: it follows that it too, like the sensitive part, can
have no nature of its own, other than that of having a certain capacity. Thus
that in the soul which is called mind (by mind I mean that whereby the soul
thinks and judges) is, before it thinks, not actually any real thing. For this
reason it cannot reasonably be regarded as blended with the body: if so, it
would acquire some quality, e.g. warmth or cold, or even have an organ like the
sensitive faculty: as it is, it has none. It was a good idea to call the soul
'the place of forms', though (1) this description holds only of the intellective
soul, and (2) even this is the forms only potentially, not actually.

Observation of the sense-organs and their employment
reveals a distinction between the impassibility of the sensitive and that of the
intellective faculty. After strong stimulation of a sense we are less able to
exercise it than before, as e.g. in the case of a loud sound we cannot hear
easily immediately after, or in the case of a bright colour or a powerful odour
we cannot see or smell, but in the case of mind thought about an object that is
highly intelligible renders it more and not less able afterwards to think
objects that are less intelligible: the reason is that while the faculty of
sensation is dependent upon the body, mind is separable from it.

Once the mind has become each set of its possible objects,
as a man of science has, when this phrase is used of one who is actually a man
of science (this happens when he is now able to exercise the power on his own
initiative), its condition is still one of potentiality, but in a different
sense from the potentiality which preceded the acquisition of knowledge by
learning or discovery: the mind too is then able to think itself.

Since we can distinguish between a spatial magnitude and
what it is to be such, and between water and what it is to be water, and so in
many other cases (though not in all; for in certain cases the thing and its form
are identical), flesh and what it is to be flesh are discriminated either by
different faculties, or by the same faculty in two different states: for flesh
necessarily involves matter and is like what is snub-nosed, a this in a this.
Now it is by means of the sensitive faculty that we discriminate the hot and the
cold, i.e. the factors which combined in a certain ratio constitute flesh: the
essential character of flesh is apprehended by something different either wholly
separate from the sensitive faculty or related to it as a bent line to the same
line when it has been straightened out.

Again in the case of abstract objects what is straight is
analogous to what is snub-nosed; for it necessarily implies a continuum as its
matter: its constitutive essence is different, if we may distinguish between
straightness and what is straight: let us take it to be two-ness. It must be
apprehended, therefore, by a different power or by the same power in a different
state. To sum up, in so far as the realities it knows are capable of being
separated from their matter, so it is also with the powers of mind.

The problem might be suggested: if thinking is a passive
affection, then if mind is simple and impassible and has nothing in common with
anything else, as Anaxagoras says, how can it come to think at all? For
interaction between two factors is held to require a precedent community of
nature between the factors. Again it might be asked, is mind a possible object
of thought to itself? For if mind is thinkable per se and what is thinkable is
in kind one and the same, then either (a) mind will belong to everything, or (b)
mind will contain some element common to it with all other realities which makes
them all thinkable.

(1) Have not we already disposed of the difficulty about
interaction involving a common element, when we said that mind is in a sense
potentially whatever is thinkable, though actually it is nothing until it has
thought? What it thinks must be in it just as characters may be said to be on a
writingtablet on which as yet nothing actually stands written: this is exactly
what happens with mind.

(Mind is itself thinkable in exactly the same way as its
objects are. For (a) in the case of objects which involve no matter, what thinks
and what is thought are identical; for speculative knowledge and its object are
identical. (Why mind is not always thinking we must consider later.) (b) In the
case of those which contain matter each of the objects of thought is only
potentially present. It follows that while they will not have mind in them (for
mind is a potentiality of them only in so far as they are capable of being
disengaged from matter) mind may yet be thinkable.

5

Since in every class of things, as in nature as a whole, we
find two factors involved, (1) a matter which is potentially all the particulars
included in the class, (2) a cause which is productive in the sense that it
makes them all (the latter standing to the former, as e.g. an art to its
material), these distinct elements must likewise be found within the soul.

And in fact mind as we have described it is what it is what
it is by virtue of becoming all things, while there is another which is what it
is by virtue of making all things: this is a sort of positive state like light;
for in a sense light makes potential colours into actual colours.

Mind in this sense of it is separable, impassible, unmixed,
since it is in its essential nature activity (for always the active is superior
to the passive factor, the originating force to the matter which it forms).

Actual knowledge is identical with its object: in the
individual, potential knowledge is in time prior to actual knowledge, but in the
universe as a whole it is not prior even in time. Mind is not at one time
knowing and at another not. When mind is set free from its present conditions it
appears as just what it is and nothing more: this alone is immortal and eternal
(we do not, however, remember its former activity because, while mind in this
sense is impassible, mind as passive is destructible), and without it nothing
thinks.

6

The thinking then of the simple objects of thought is found
in those cases where falsehood is impossible: where the alternative of true or
false applies, there we always find a putting together of objects of thought in
a quasi-unity. As Empedocles said that 'where heads of many a creature sprouted
without necks' they afterwards by Love's power were combined, so here too
objects of thought which were given separate are combined, e.g. 'incommensurate'
and 'diagonal': if the combination be of objects past or future the combination
of thought includes in its content the date. For falsehood always involves a
synthesis; for even if you assert that what is white is not white you have
included not white in a synthesis. It is possible also to call all these cases
division as well as combination. However that may be, there is not only the true
or false assertion that Cleon is white but also the true or false assertion that
he was or will he white. In each and every case that which unifies is mind.

Since the word 'simple' has two senses, i.e. may mean
either (a) 'not capable of being divided' or (b) 'not actually divided', there
is nothing to prevent mind from knowing what is undivided, e.g. when it
apprehends a length (which is actually undivided) and that in an undivided time;
for the time is divided or undivided in the same manner as the line. It is not
possible, then, to tell what part of the line it was apprehending in each half
of the time: the object has no actual parts until it has been divided: if in
thought you think each half separately, then by the same act you divide the time
also, the half-lines becoming as it were new wholes of length. But if you think
it as a whole consisting of these two possible parts, then also you think it in
a time which corresponds to both parts together. (But what is not quantitatively
but qualitatively simple is thought in a simple time and by a simple act of the
soul.)

But that which mind thinks and the time in which it thinks
are in this case divisible only incidentally and not as such. For in them too
there is something indivisible (though, it may be, not isolable) which gives
unity to the time and the whole of length; and this is found equally in every
continuum whether temporal or spatial.

Points and similar instances of things that divide,
themselves being indivisible, are realized in consciousness in the same manner
as privations.

A similar account may be given of all other cases, e.g. how
evil or black is cognized; they are cognized, in a sense, by means of their
contraries. That which cognizes must have an element of potentiality in its
being, and one of the contraries must be in it. But if there is anything that
has no contrary, then it knows itself and is actually and possesses independent
existence.

Assertion is the saying of something concerning something,
e.g. affirmation, and is in every case either true or false: this is not always
the case with mind: the thinking of the definition in the sense of the
constitutive essence is never in error nor is it the assertion of something
concerning something, but, just as while the seeing of the special object of
sight can never be in error, the belief that the white object seen is a man may
be mistaken, so too in the case of objects which are without matter.

7

Actual knowledge is identical with its object: potential
knowledge in the individual is in time prior to actual knowledge but in the
universe it has no priority even in time; for all things that come into being
arise from what actually is. In the case of sense clearly the sensitive faculty
already was potentially what the object makes it to be actually; the faculty is
not affected or altered. This must therefore be a different kind from movement;
for movement is, as we saw, an activity of what is imperfect, activity in the
unqualified sense, i.e. that of what has been perfected, is different from
movement.

To perceive then is like bare asserting or knowing; but
when the object is pleasant or painful, the soul makes a quasi-affirmation or
negation, and pursues or avoids the object. To feel pleasure or pain is to act
with the sensitive mean towards what is good or bad as such. Both avoidance and
appetite when actual are identical with this: the faculty of appetite and
avoidance are not different, either from one another or from the faculty of
sense-perception; but their being is different.

To the thinking soul images serve as if they were contents
of perception (and when it asserts or denies them to be good or bad it avoids or
pursues them). That is why the soul never thinks without an image. The process
is like that in which the air modifies the pupil in this or that way and the
pupil transmits the modification to some third thing (and similarly in hearing),
while the ultimate point of arrival is one, a single mean, with different
manners of being.

With what part of itself the soul discriminates sweet from
hot I have explained before and must now describe again as follows: That with
which it does so is a sort of unity, but in the way just mentioned, i.e. as a
connecting term. And the two faculties it connects, being one by analogy and
numerically, are each to each as the qualities discerned are to one another (for
what difference does it make whether we raise the problem of discrimination
between disparates or between contraries, e.g. white and black?). Let then C be
to D as is to B: it follows alternando that C: A:: D: B. If then C and D belong
to one subject, the case will be the same with them as with and B; and B form a
single identity with different modes of being; so too will the former pair. The
same reasoning holds if be sweet and B white.

The faculty of thinking then thinks the forms in the
images, and as in the former case what is to be pursued or avoided is marked out
for it, so where there is no sensation and it is engaged upon the images it is
moved to pursuit or avoidance. E.g.. perceiving by sense that the beacon is
fire, it recognizes in virtue of the general faculty of sense that it signifies
an enemy, because it sees it moving; but sometimes by means of the images or
thoughts which are within the soul, just as if it were seeing, it calculates and
deliberates what is to come by reference to what is present; and when it makes a
pronouncement, as in the case of sensation it pronounces the object to be
pleasant or painful, in this case it avoids or persues and so generally in cases
of action.

That too which involves no action, i.e. that which is true
or false, is in the same province with what is good or bad: yet they differ in
this, that the one set imply and the other do not a reference to a particular
person.

The so-called abstract objects the mind thinks just as, if
one had thought of the snubnosed not as snub-nosed but as hollow, one would have
thought of an actuality without the flesh in which it is embodied: it is thus
that the mind when it is thinking the objects of Mathematics thinks as separate
elements which do not exist separate. In every case the mind which is actively
thinking is the objects which it thinks. Whether it is possible for it while not
existing separate from spatial conditions to think anything that is separate, or
not, we must consider later.

8

Let us now summarize our results about soul, and repeat
that the soul is in a way all existing things; for existing things are either
sensible or thinkable, and knowledge is in a way what is knowable, and sensation
is in a way what is sensible: in what way we must inquire.

Knowledge and sensation are divided to correspond with the
realities, potential knowledge and sensation answering to potentialities, actual
knowledge and sensation to actualities. Within the soul the faculties of
knowledge and sensation are potentially these objects, the one what is knowable,
the other what is sensible. They must be either the things themselves or their
forms. The former alternative is of course impossible: it is not the stone which
is present in the soul but its form.

It follows that the soul is analogous to the hand; for as
the hand is a tool of tools, so the mind is the form of forms and sense the form
of sensible things.

Since according to common agreement there is nothing
outside and separate in existence from sensible spatial magnitudes, the objects
of thought are in the sensible forms, viz. both the abstract objects and all the
states and affections of sensible things. Hence (1) no one can learn or
understand anything in the absence of sense, and (when the mind is actively
aware of anything it is necessarily aware of it along with an image; for images
are like sensuous contents except in that they contain no matter.

Imagination is different from assertion and denial; for
what is true or false involves a synthesis of concepts. In what will the primary
concepts differ from images? Must we not say that neither these nor even our
other concepts are images, though they necessarily involve them?

9

The soul of animals is characterized by two faculties, (a)
the faculty of discrimination which is the work of thought and sense, and (b)
the faculty of originating local movement. Sense and mind we have now
sufficiently examined. Let us next consider what it is in the soul which
originates movement. Is it a single part of the soul separate either spatially
or in definition? Or is it the soul as a whole? If it is a part, is that part
different from those usually distinguished or already mentioned by us, or is it
one of them? The problem at once presents itself, in what sense we are to speak
of parts of the soul, or how many we should distinguish. For in a sense there is
an infinity of parts: it is not enough to distinguish, with some thinkers, the
calculative, the passionate, and the desiderative, or with others the rational
and the irrational; for if we take the dividing lines followed by these thinkers
we shall find parts far more distinctly separated from one another than these,
namely those we have just mentioned: (1) the nutritive, which belongs both to
plants and to all animals, and (2) the sensitive, which cannot easily be classed
as either irrational or rational; further (3) the imaginative, which is, in its
being, different from all, while it is very hard to say with which of the others
it is the same or not the same, supposing we determine to posit separate parts
in the soul; and lastly (4) the appetitive, which would seem to be distinct both
in definition and in power from all hitherto enumerated.

It is absurd to break up the last-mentioned faculty: as
these thinkers do, for wish is found in the calculative part and desire and
passion in the irrational; and if the soul is tripartite appetite will be found
in all three parts. Turning our attention to the present object of discussion,
let us ask what that is which originates local movement of the animal.

The movement of growth and decay, being found in all living
things, must be attributed to the faculty of reproduction and nutrition, which
is common to all: inspiration and expiration, sleep and waking, we must consider
later: these too present much difficulty: at present we must consider local
movement, asking what it is that originates forward movement in the animal.

That it is not the nutritive faculty is obvious; for this
kind of movement is always for an end and is accompanied either by imagination
or by appetite; for no animal moves except by compulsion unless it has an
impulse towards or away from an object. Further, if it were the nutritive
faculty, even plants would have been capable of originating such movement and
would have possessed the organs necessary to carry it out. Similarly it cannot
be the sensitive faculty either; for there are many animals which have
sensibility but remain fast and immovable throughout their lives.

If then Nature never makes anything without a purpose and
never leaves out what is necessary (except in the case of mutilated or imperfect
growths; and that here we have neither mutilation nor imperfection may be argued
from the facts that such animals (a) can reproduce their species and (b) rise to
completeness of nature and decay to an end), it follows that, had they been
capable of originating forward movement, they would have possessed the organs
necessary for that purpose. Further, neither can the calculative faculty or what
is called 'mind' be the cause of such movement; for mind as speculative never
thinks what is practicable, it never says anything about an object to be avoided
or pursued, while this movement is always in something which is avoiding or
pursuing an object. No, not even when it is aware of such an object does it at
once enjoin pursuit or avoidance of it; e.g. the mind often thinks of something
terrifying or pleasant without enjoining the emotion of fear. It is the heart
that is moved (or in the case of a pleasant object some other part). Further,
even when the mind does command and thought bids us pursue or avoid something,
sometimes no movement is produced; we act in accordance with desire, as in the
case of moral weakness. And, generally, we observe that the possessor of medical
knowledge is not necessarily healing, which shows that something else is
required to produce action in accordance with knowledge; the knowledge alone is
not the cause. Lastly, appetite too is incompetent to account fully for
movement; for those who successfully resist temptation have appetite and desire
and yet follow mind and refuse to enact that for which they have appetite.

10

These two at all events appear to be sources of movement:
appetite and mind (if one may venture to regard imagination as a kind of
thinking; for many men follow their imaginations contrary to knowledge, and in
all animals other than man there is no thinking or calculation but only
imagination).

Both of these then are capable of originating local
movement, mind and appetite: (1) mind, that is, which calculates means to an
end, i.e. mind practical (it differs from mind speculative in the character of
its end); while (2) appetite is in every form of it relative to an end: for that
which is the object of appetite is the stimulant of mind practical; and that
which is last in the process of thinking is the beginning of the action. It
follows that there is a justification for regarding these two as the sources of
movement, i.e. appetite and practical thought; for the object of appetite starts
a movement and as a result of that thought gives rise to movement, the object of
appetite being it a source of stimulation. So too when imagination originates
movement, it necessarily involves appetite.

That which moves therefore is a single faculty and the
faculty of appetite; for if there had been two sources of movement-mind and
appetite-they would have produced movement in virtue of some common character.
As it is, mind is never found producing movement without appetite (for wish is a
form of appetite; and when movement is produced according to calculation it is
also according to wish), but appetite can originate movement contrary to
calculation, for desire is a form of appetite. Now mind is always right, but
appetite and imagination may be either right or wrong. That is why, though in
any case it is the object of appetite which originates movement, this object may
be either the real or the apparent good. To produce movement the object must be
more than this: it must be good that can be brought into being by action; and
only what can be otherwise than as it is can thus be brought into being. That
then such a power in the soul as has been described, i.e. that called appetite,
originates movement is clear. Those who distinguish parts in the soul, if they
distinguish and divide in accordance with differences of power, find themselves
with a very large number of parts, a nutritive, a sensitive, an intellective, a
deliberative, and now an appetitive part; for these are more different from one
another than the faculties of desire and passion.

Since appetites run counter to one another, which happens
when a principle of reason and a desire are contrary and is possible only in
beings with a sense of time (for while mind bids us hold back because of what is
future, desire is influenced by what is just at hand: a pleasant object which is
just at hand presents itself as both pleasant and good, without condition in
either case, because of want of foresight into what is farther away in time), it
follows that while that which originates movement must be specifically one, viz.
the faculty of appetite as such (or rather farthest back of all the object of
that faculty; for it is it that itself remaining unmoved originates the movement
by being apprehended in thought or imagination), the things that originate
movement are numerically many.

All movement involves three factors, (1) that which
originates the movement, (2) that by means of which it originates it, and (3)
that which is moved. The expression 'that which originates the movement' is
ambiguous: it may mean either (a) something which itself is unmoved or (b) that
which at once moves and is moved. Here that which moves without itself being
moved is the realizable good, that which at once moves and is moved is the
faculty of appetite (for that which is influenced by appetite so far as it is
actually so influenced is set in movement, and appetite in the sense of actual
appetite is a kind of movement), while that which is in motion is the animal.
The instrument which appetite employs to produce movement is no longer psychical
but bodily: hence the examination of it falls within the province of the
functions common to body and soul. To state the matter summarily at present,
that which is the instrument in the production of movement is to be found where
a beginning and an end coincide as e.g. in a ball and socket joint; for there
the convex and the concave sides are respectively an end and a beginning (that
is why while the one remains at rest, the other is moved): they are separate in
definition but not separable spatially. For everything is moved by pushing and
pulling. Hence just as in the case of a wheel, so here there must be a point
which remains at rest, and from that point the movement must originate.

To sum up, then, and repeat what I have said, inasmuch as
an animal is capable of appetite it is capable of self-movement; it is not
capable of appetite without possessing imagination; and all imagination is
either (1) calculative or (2) sensitive. In the latter an animals, and not only
man, partake.

11

We must consider also in the case of imperfect animals, sc.
those which have no sense but touch, what it is that in them originates
movement. Can they have imagination or not? or desire? Clearly they have
feelings of pleasure and pain, and if they have these they must have desire. But
how can they have imagination? Must not we say that, as their movements are
indefinite, they have imagination and desire, but indefinitely?

Sensitive imagination, as we have said, is found in all
animals, deliberative imagination only in those that are calculative: for
whether this or that shall be enacted is already a task requiring calculation;
and there must be a single standard to measure by, for that is pursued which is
greater. It follows that what acts in this way must be able to make a unity out
of several images.

This is the reason why imagination is held not to involve
opinion, in that it does not involve opinion based on inference, though opinion
involves imagination. Hence appetite contains no deliberative element. Sometimes
it overpowers wish and sets it in movement: at times wish acts thus upon
appetite, like one sphere imparting its movement to another, or appetite acts
thus upon appetite, i.e. in the condition of moral weakness (though by nature
the higher faculty is always more authoritative and gives rise to movement).
Thus three modes of movement are possible.

The faculty of knowing is never moved but remains at rest.
Since the one premiss or judgement is universal and the other deals with the
particular (for the first tells us that such and such a kind of man should do
such and such a kind of act, and the second that this is an act of the kind
meant, and I a person of the type intended), it is the latter opinion that
really originates movement, not the universal; or rather it is both, but the one
does so while it remains in a state more like rest, while the other partakes in
movement.

12

The nutritive soul then must be possessed by everything
that is alive, and every such thing is endowed with soul from its birth to its
death. For what has been born must grow, reach maturity, and decay-all of which
are impossible without nutrition. Therefore the nutritive faculty must be found
in everything that grows and decays.

But sensation need not be found in all things that live.
For it is impossible for touch to belong either (1) to those whose body is
uncompounded or (2) to those which are incapable of taking in the forms without
their matter.

But animals must be endowed with sensation, since Nature
does nothing in vain. For all things that exist by Nature are means to an end,
or will be concomitants of means to an end. Every body capable of forward
movement would, if unendowed with sensation, perish and fail to reach its end,
which is the aim of Nature; for how could it obtain nutriment? Stationary living
things, it is true, have as their nutriment that from which they have arisen;
but it is not possible that a body which is not stationary but produced by
generation should have a soul and a discerning mind without also having
sensation. (Nor yet even if it were not produced by generation. Why should it
not have sensation? Because it were better so either for the body or for the
soul? But clearly it would not be better for either: the absence of sensation
will not enable the one to think better or the other to exist better.) Therefore
no body which is not stationary has soul without sensation.

But if a body has sensation, it must be either simple or
compound. And simple it cannot be; for then it could not have touch, which is
indispensable. This is clear from what follows. An animal is a body with soul in
it: every body is tangible, i.e. perceptible by touch; hence necessarily, if an
animal is to survive, its body must have tactual sensation. All the other
senses, e.g. smell, sight, hearing, apprehend through media; but where there is
immediate contact the animal, if it has no sensation, will be unable to avoid
some things and take others, and so will find it impossible to survive. That is
why taste also is a sort of touch; it is relative to nutriment, which is just
tangible body; whereas sound, colour, and odour are innutritious, and further
neither grow nor decay. Hence it is that taste also must be a sort of touch,
because it is the sense for what is tangible and nutritious.

Both these senses, then, are indispensable to the animal,
and it is clear that without touch it is impossible for an animal to be. All the
other senses subserve well-being and for that very reason belong not to any and
every kind of animal, but only to some, e.g. those capable of forward movement
must have them; for, if they are to survive, they must perceive not only by
immediate contact but also at a distance from the object. This will be possible
if they can perceive through a medium, the medium being affected and moved by
the perceptible object, and the animal by the medium. just as that which
produces local movement causes a change extending to a certain point, and that
which gave an impulse causes another to produce a new impulse so that the
movement traverses a medium the first mover impelling without being impelled,
the last moved being impelled without impelling, while the medium (or media, for
there are many) is both-so is it also in the case of alteration, except that the
agent produces produces it without the patient's changing its place. Thus if an
object is dipped into wax, the movement goes on until submersion has taken
place, and in stone it goes no distance at all, while in water the disturbance
goes far beyond the object dipped: in air the disturbance is propagated farthest
of all, the air acting and being acted upon, so long as it maintains an unbroken
unity. That is why in the case of reflection it is better, instead of saying
that the sight issues from the eye and is reflected, to say that the air, so
long as it remains one, is affected by the shape and colour. On a smooth surface
the air possesses unity; hence it is that it in turn sets the sight in motion,
just as if the impression on the wax were transmitted as far as the wax extends.

13

It is clear that the body of an animal cannot be simple,
i.e. consist of one element such as fire or air. For without touch it is
impossible to have any other sense; for every body that has soul in it must, as
we have said, be capable of touch. All the other elements with the exception of
earth can constitute organs of sense, but all of them bring about perception
only through something else, viz. through the media. Touch takes place by direct
contact with its objects, whence also its name. All the other organs of sense,
no doubt, perceive by contact, only the contact is mediate: touch alone
perceives by immediate contact. Consequently no animal body can consist of these
other elements.

Nor can it consist solely of earth. For touch is as it were
a mean between all tangible qualities, and its organ is capable of receiving not
only all the specific qualities which characterize earth, but also the hot and
the cold and all other tangible qualities whatsoever. That is why we have no
sensation by means of bones, hair, &c., because they consist of earth. So
too plants, because they consist of earth, have no sensation. Without touch
there can be no other sense, and the organ of touch cannot consist of earth or
of any other single element.

It is evident, therefore, that the loss of this one sense
alone must bring about the death of an animal. For as on the one hand nothing
which is not an animal can have this sense, so on the other it is the only one
which is indispensably necessary to what is an animal. This explains, further,
the following difference between the other senses and touch. In the case of all
the others excess of intensity in the qualities which they apprehend, i.e.
excess of intensity in colour, sound, and smell, destroys not the but only the
organs of the sense (except incidentally, as when the sound is accompanied by an
impact or shock, or where through the objects of sight or of smell certain other
things are set in motion, which destroy by contact); flavour also destroys only
in so far as it is at the same time tangible. But excess of intensity in
tangible qualities, e.g. heat, cold, or hardness, destroys the animal itself. As
in the case of every sensible quality excess destroys the organ, so here what is
tangible destroys touch, which is the essential mark of life; for it has been
shown that without touch it is impossible for an animal to be. That is why
excess in intensity of tangible qualities destroys not merely the organ, but the
animal itself, because this is the only sense which it must have.

All the other senses are necessary to animals, as we have
said, not for their being, but for their well-being. Such, e.g. is sight, which,
since it lives in air or water, or generally in what is pellucid, it must have
in order to see, and taste because of what is pleasant or painful to it, in
order that it may perceive these qualities in its nutriment and so may desire to
be set in motion, and hearing that it may have communication made to it, and a
tongue that it may communicate with its fellows.